13 files changed, 1549 insertions, 1213 deletions

diff --git a/core/string/node_path.cpp b/core/string/node_path.cpp
index 8ae2efb787..fdc72bc8dc 100644
--- a/core/string/node_path.cpp
+++ b/core/string/node_path.cpp
@@ -215,7 +215,10 @@ StringName NodePath::get_concatenated_names() const {
 		String concatenated;
 		const StringName *sn = data->path.ptr();
 		for (int i = 0; i < pc; i++) {
-			concatenated += i == 0 ? sn[i].operator String() : "/" + sn[i];
+			if (i > 0) {
+				concatenated += "/";
+			}
+			concatenated += sn[i].operator String();
 		}
 		data->concatenated_path = concatenated;
 	}
@@ -230,7 +233,10 @@ StringName NodePath::get_concatenated_subnames() const {
 		String concatenated;
 		const StringName *ssn = data->subpath.ptr();
 		for (int i = 0; i < spc; i++) {
-			concatenated += i == 0 ? ssn[i].operator String() : ":" + ssn[i];
+			if (i > 0) {
+				concatenated += ":";
+			}
+			concatenated += ssn[i].operator String();
 		}
 		data->concatenated_subpath = concatenated;
 	}
diff --git a/core/string/string_name.cpp b/core/string/string_name.cpp
index 658297d805..5d59d65f92 100644
--- a/core/string/string_name.cpp
+++ b/core/string/string_name.cpp
@@ -39,19 +39,10 @@ StaticCString StaticCString::create(const char *p_ptr) {
 	return scs;
 }
 
-StringName::_Data *StringName::_table[STRING_TABLE_LEN];
-
 StringName _scs_create(const char *p_chr, bool p_static) {
 	return (p_chr[0] ? StringName(StaticCString::create(p_chr), p_static) : StringName());
 }
 
-bool StringName::configured = false;
-Mutex StringName::mutex;
-
-#ifdef DEBUG_ENABLED
-bool StringName::debug_stringname = false;
-#endif
-
 void StringName::setup() {
 	ERR_FAIL_COND(configured);
 	for (int i = 0; i < STRING_TABLE_LEN; i++) {
diff --git a/core/string/string_name.h b/core/string/string_name.h
index 89b4c07e0e..0eb98cf64b 100644
--- a/core/string/string_name.h
+++ b/core/string/string_name.h
@@ -67,7 +67,7 @@ class StringName {
 		_Data() {}
 	};
 
-	static _Data *_table[STRING_TABLE_LEN];
+	static inline _Data *_table[STRING_TABLE_LEN];
 
 	_Data *_data = nullptr;
 
@@ -75,10 +75,10 @@ class StringName {
 	friend void register_core_types();
 	friend void unregister_core_types();
 	friend class Main;
-	static Mutex mutex;
+	static inline Mutex mutex;
 	static void setup();
 	static void cleanup();
-	static bool configured;
+	static inline bool configured = false;
 #ifdef DEBUG_ENABLED
 	struct DebugSortReferences {
 		bool operator()(const _Data *p_left, const _Data *p_right) const {
@@ -86,7 +86,7 @@ class StringName {
 		}
 	};
 
-	static bool debug_stringname;
+	static inline bool debug_stringname = false;
 #endif
 
 	StringName(_Data *p_data) { _data = p_data; }
diff --git a/core/string/translation.compat.inc b/core/string/translation.compat.inc
index d792d4a6fc..68bd1831e4 100644
--- a/core/string/translation.compat.inc
+++ b/core/string/translation.compat.inc
@@ -38,9 +38,4 @@ void Translation::_bind_compatibility_methods() {
 	ClassDB::bind_compatibility_method(D_METHOD("erase_message", "src_message", "context"), &Translation::erase_message, DEFVAL(""));
 }
 
-void TranslationServer::_bind_compatibility_methods() {
-	ClassDB::bind_compatibility_method(D_METHOD("translate", "message", "context"), &TranslationServer::translate, DEFVAL(""));
-	ClassDB::bind_compatibility_method(D_METHOD("translate_plural", "message", "plural_message", "n", "context"), &TranslationServer::translate_plural, DEFVAL(""));
-}
-
 #endif
diff --git a/core/string/translation.cpp b/core/string/translation.cpp
index 344fe42fa0..33d4a1bcde 100644
--- a/core/string/translation.cpp
+++ b/core/string/translation.cpp
@@ -31,14 +31,9 @@
 #include "translation.h"
 #include "translation.compat.inc"
 
-#include "core/config/project_settings.h"
-#include "core/io/resource_loader.h"
 #include "core/os/os.h"
-#include "core/string/locales.h"
-
-#ifdef TOOLS_ENABLED
-#include "main/main.h"
-#endif
+#include "core/os/thread.h"
+#include "core/string/translation_server.h"
 
 Dictionary Translation::_get_messages() const {
 	Dictionary d;
@@ -173,915 +168,3 @@ void Translation::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::DICTIONARY, "messages", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR | PROPERTY_USAGE_INTERNAL), "_set_messages", "_get_messages");
 	ADD_PROPERTY(PropertyInfo(Variant::STRING, "locale"), "set_locale", "get_locale");
 }
-
-///////////////////////////////////////////////
-
-struct _character_accent_pair {
-	const char32_t character;
-	const char32_t *accented_character;
-};
-
-static _character_accent_pair _character_to_accented[] = {
-	{ 'A', U"Å" },
-	{ 'B', U"ß" },
-	{ 'C', U"Ç" },
-	{ 'D', U"Ð" },
-	{ 'E', U"É" },
-	{ 'F', U"F́" },
-	{ 'G', U"Ĝ" },
-	{ 'H', U"Ĥ" },
-	{ 'I', U"Ĩ" },
-	{ 'J', U"Ĵ" },
-	{ 'K', U"ĸ" },
-	{ 'L', U"Ł" },
-	{ 'M', U"Ḿ" },
-	{ 'N', U"й" },
-	{ 'O', U"Ö" },
-	{ 'P', U"Ṕ" },
-	{ 'Q', U"Q́" },
-	{ 'R', U"Ř" },
-	{ 'S', U"Ŝ" },
-	{ 'T', U"Ŧ" },
-	{ 'U', U"Ũ" },
-	{ 'V', U"Ṽ" },
-	{ 'W', U"Ŵ" },
-	{ 'X', U"X́" },
-	{ 'Y', U"Ÿ" },
-	{ 'Z', U"Ž" },
-	{ 'a', U"á" },
-	{ 'b', U"ḅ" },
-	{ 'c', U"ć" },
-	{ 'd', U"d́" },
-	{ 'e', U"é" },
-	{ 'f', U"f́" },
-	{ 'g', U"ǵ" },
-	{ 'h', U"h̀" },
-	{ 'i', U"í" },
-	{ 'j', U"ǰ" },
-	{ 'k', U"ḱ" },
-	{ 'l', U"ł" },
-	{ 'm', U"m̀" },
-	{ 'n', U"ή" },
-	{ 'o', U"ô" },
-	{ 'p', U"ṕ" },
-	{ 'q', U"q́" },
-	{ 'r', U"ŕ" },
-	{ 's', U"š" },
-	{ 't', U"ŧ" },
-	{ 'u', U"ü" },
-	{ 'v', U"ṽ" },
-	{ 'w', U"ŵ" },
-	{ 'x', U"x́" },
-	{ 'y', U"ý" },
-	{ 'z', U"ź" },
-};
-
-Vector<TranslationServer::LocaleScriptInfo> TranslationServer::locale_script_info;
-
-HashMap<String, String> TranslationServer::language_map;
-HashMap<String, String> TranslationServer::script_map;
-HashMap<String, String> TranslationServer::locale_rename_map;
-HashMap<String, String> TranslationServer::country_name_map;
-HashMap<String, String> TranslationServer::variant_map;
-HashMap<String, String> TranslationServer::country_rename_map;
-
-void TranslationServer::init_locale_info() {
-	// Init locale info.
-	language_map.clear();
-	int idx = 0;
-	while (language_list[idx][0] != nullptr) {
-		language_map[language_list[idx][0]] = String::utf8(language_list[idx][1]);
-		idx++;
-	}
-
-	// Init locale-script map.
-	locale_script_info.clear();
-	idx = 0;
-	while (locale_scripts[idx][0] != nullptr) {
-		LocaleScriptInfo info;
-		info.name = locale_scripts[idx][0];
-		info.script = locale_scripts[idx][1];
-		info.default_country = locale_scripts[idx][2];
-		Vector<String> supported_countries = String(locale_scripts[idx][3]).split(",", false);
-		for (int i = 0; i < supported_countries.size(); i++) {
-			info.supported_countries.insert(supported_countries[i]);
-		}
-		locale_script_info.push_back(info);
-		idx++;
-	}
-
-	// Init supported script list.
-	script_map.clear();
-	idx = 0;
-	while (script_list[idx][0] != nullptr) {
-		script_map[script_list[idx][1]] = String::utf8(script_list[idx][0]);
-		idx++;
-	}
-
-	// Init regional variant map.
-	variant_map.clear();
-	idx = 0;
-	while (locale_variants[idx][0] != nullptr) {
-		variant_map[locale_variants[idx][0]] = locale_variants[idx][1];
-		idx++;
-	}
-
-	// Init locale renames.
-	locale_rename_map.clear();
-	idx = 0;
-	while (locale_renames[idx][0] != nullptr) {
-		if (!String(locale_renames[idx][1]).is_empty()) {
-			locale_rename_map[locale_renames[idx][0]] = locale_renames[idx][1];
-		}
-		idx++;
-	}
-
-	// Init country names.
-	country_name_map.clear();
-	idx = 0;
-	while (country_names[idx][0] != nullptr) {
-		country_name_map[String(country_names[idx][0])] = String::utf8(country_names[idx][1]);
-		idx++;
-	}
-
-	// Init country renames.
-	country_rename_map.clear();
-	idx = 0;
-	while (country_renames[idx][0] != nullptr) {
-		if (!String(country_renames[idx][1]).is_empty()) {
-			country_rename_map[country_renames[idx][0]] = country_renames[idx][1];
-		}
-		idx++;
-	}
-}
-
-String TranslationServer::standardize_locale(const String &p_locale) const {
-	return _standardize_locale(p_locale, false);
-}
-
-String TranslationServer::_standardize_locale(const String &p_locale, bool p_add_defaults) const {
-	// Replaces '-' with '_' for macOS style locales.
-	String univ_locale = p_locale.replace("-", "_");
-
-	// Extract locale elements.
-	String lang_name, script_name, country_name, variant_name;
-	Vector<String> locale_elements = univ_locale.get_slice("@", 0).split("_");
-	lang_name = locale_elements[0];
-	if (locale_elements.size() >= 2) {
-		if (locale_elements[1].length() == 4 && is_ascii_upper_case(locale_elements[1][0]) && is_ascii_lower_case(locale_elements[1][1]) && is_ascii_lower_case(locale_elements[1][2]) && is_ascii_lower_case(locale_elements[1][3])) {
-			script_name = locale_elements[1];
-		}
-		if (locale_elements[1].length() == 2 && is_ascii_upper_case(locale_elements[1][0]) && is_ascii_upper_case(locale_elements[1][1])) {
-			country_name = locale_elements[1];
-		}
-	}
-	if (locale_elements.size() >= 3) {
-		if (locale_elements[2].length() == 2 && is_ascii_upper_case(locale_elements[2][0]) && is_ascii_upper_case(locale_elements[2][1])) {
-			country_name = locale_elements[2];
-		} else if (variant_map.has(locale_elements[2].to_lower()) && variant_map[locale_elements[2].to_lower()] == lang_name) {
-			variant_name = locale_elements[2].to_lower();
-		}
-	}
-	if (locale_elements.size() >= 4) {
-		if (variant_map.has(locale_elements[3].to_lower()) && variant_map[locale_elements[3].to_lower()] == lang_name) {
-			variant_name = locale_elements[3].to_lower();
-		}
-	}
-
-	// Try extract script and variant from the extra part.
-	Vector<String> script_extra = univ_locale.get_slice("@", 1).split(";");
-	for (int i = 0; i < script_extra.size(); i++) {
-		if (script_extra[i].to_lower() == "cyrillic") {
-			script_name = "Cyrl";
-			break;
-		} else if (script_extra[i].to_lower() == "latin") {
-			script_name = "Latn";
-			break;
-		} else if (script_extra[i].to_lower() == "devanagari") {
-			script_name = "Deva";
-			break;
-		} else if (variant_map.has(script_extra[i].to_lower()) && variant_map[script_extra[i].to_lower()] == lang_name) {
-			variant_name = script_extra[i].to_lower();
-		}
-	}
-
-	// Handles known non-ISO language names used e.g. on Windows.
-	if (locale_rename_map.has(lang_name)) {
-		lang_name = locale_rename_map[lang_name];
-	}
-
-	// Handle country renames.
-	if (country_rename_map.has(country_name)) {
-		country_name = country_rename_map[country_name];
-	}
-
-	// Remove unsupported script codes.
-	if (!script_map.has(script_name)) {
-		script_name = "";
-	}
-
-	// Add script code base on language and country codes for some ambiguous cases.
-	if (p_add_defaults) {
-		if (script_name.is_empty()) {
-			for (int i = 0; i < locale_script_info.size(); i++) {
-				const LocaleScriptInfo &info = locale_script_info[i];
-				if (info.name == lang_name) {
-					if (country_name.is_empty() || info.supported_countries.has(country_name)) {
-						script_name = info.script;
-						break;
-					}
-				}
-			}
-		}
-		if (!script_name.is_empty() && country_name.is_empty()) {
-			// Add conntry code based on script for some ambiguous cases.
-			for (int i = 0; i < locale_script_info.size(); i++) {
-				const LocaleScriptInfo &info = locale_script_info[i];
-				if (info.name == lang_name && info.script == script_name) {
-					country_name = info.default_country;
-					break;
-				}
-			}
-		}
-	}
-
-	// Combine results.
-	String out = lang_name;
-	if (!script_name.is_empty()) {
-		out = out + "_" + script_name;
-	}
-	if (!country_name.is_empty()) {
-		out = out + "_" + country_name;
-	}
-	if (!variant_name.is_empty()) {
-		out = out + "_" + variant_name;
-	}
-	return out;
-}
-
-int TranslationServer::compare_locales(const String &p_locale_a, const String &p_locale_b) const {
-	String locale_a = _standardize_locale(p_locale_a, true);
-	String locale_b = _standardize_locale(p_locale_b, true);
-
-	if (locale_a == locale_b) {
-		// Exact match.
-		return 10;
-	}
-
-	Vector<String> locale_a_elements = locale_a.split("_");
-	Vector<String> locale_b_elements = locale_b.split("_");
-	if (locale_a_elements[0] == locale_b_elements[0]) {
-		// Matching language, both locales have extra parts.
-		// Return number of matching elements.
-		int matching_elements = 1;
-		for (int i = 1; i < locale_a_elements.size(); i++) {
-			for (int j = 1; j < locale_b_elements.size(); j++) {
-				if (locale_a_elements[i] == locale_b_elements[j]) {
-					matching_elements++;
-				}
-			}
-		}
-		return matching_elements;
-	} else {
-		// No match.
-		return 0;
-	}
-}
-
-String TranslationServer::get_locale_name(const String &p_locale) const {
-	String lang_name, script_name, country_name;
-	Vector<String> locale_elements = standardize_locale(p_locale).split("_");
-	lang_name = locale_elements[0];
-	if (locale_elements.size() >= 2) {
-		if (locale_elements[1].length() == 4 && is_ascii_upper_case(locale_elements[1][0]) && is_ascii_lower_case(locale_elements[1][1]) && is_ascii_lower_case(locale_elements[1][2]) && is_ascii_lower_case(locale_elements[1][3])) {
-			script_name = locale_elements[1];
-		}
-		if (locale_elements[1].length() == 2 && is_ascii_upper_case(locale_elements[1][0]) && is_ascii_upper_case(locale_elements[1][1])) {
-			country_name = locale_elements[1];
-		}
-	}
-	if (locale_elements.size() >= 3) {
-		if (locale_elements[2].length() == 2 && is_ascii_upper_case(locale_elements[2][0]) && is_ascii_upper_case(locale_elements[2][1])) {
-			country_name = locale_elements[2];
-		}
-	}
-
-	String name = language_map[lang_name];
-	if (!script_name.is_empty()) {
-		name = name + " (" + script_map[script_name] + ")";
-	}
-	if (!country_name.is_empty()) {
-		name = name + ", " + country_name_map[country_name];
-	}
-	return name;
-}
-
-Vector<String> TranslationServer::get_all_languages() const {
-	Vector<String> languages;
-
-	for (const KeyValue<String, String> &E : language_map) {
-		languages.push_back(E.key);
-	}
-
-	return languages;
-}
-
-String TranslationServer::get_language_name(const String &p_language) const {
-	return language_map[p_language];
-}
-
-Vector<String> TranslationServer::get_all_scripts() const {
-	Vector<String> scripts;
-
-	for (const KeyValue<String, String> &E : script_map) {
-		scripts.push_back(E.key);
-	}
-
-	return scripts;
-}
-
-String TranslationServer::get_script_name(const String &p_script) const {
-	return script_map[p_script];
-}
-
-Vector<String> TranslationServer::get_all_countries() const {
-	Vector<String> countries;
-
-	for (const KeyValue<String, String> &E : country_name_map) {
-		countries.push_back(E.key);
-	}
-
-	return countries;
-}
-
-String TranslationServer::get_country_name(const String &p_country) const {
-	return country_name_map[p_country];
-}
-
-void TranslationServer::set_locale(const String &p_locale) {
-	String new_locale = standardize_locale(p_locale);
-	if (locale == new_locale) {
-		return;
-	}
-
-	locale = new_locale;
-	ResourceLoader::reload_translation_remaps();
-
-	if (OS::get_singleton()->get_main_loop()) {
-		OS::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_TRANSLATION_CHANGED);
-	}
-}
-
-String TranslationServer::get_locale() const {
-	return locale;
-}
-
-PackedStringArray TranslationServer::get_loaded_locales() const {
-	PackedStringArray locales;
-	for (const Ref<Translation> &E : translations) {
-		const Ref<Translation> &t = E;
-		ERR_FAIL_COND_V(t.is_null(), PackedStringArray());
-		String l = t->get_locale();
-
-		locales.push_back(l);
-	}
-
-	return locales;
-}
-
-void TranslationServer::add_translation(const Ref<Translation> &p_translation) {
-	translations.insert(p_translation);
-}
-
-void TranslationServer::remove_translation(const Ref<Translation> &p_translation) {
-	translations.erase(p_translation);
-}
-
-Ref<Translation> TranslationServer::get_translation_object(const String &p_locale) {
-	Ref<Translation> res;
-	int best_score = 0;
-
-	for (const Ref<Translation> &E : translations) {
-		const Ref<Translation> &t = E;
-		ERR_FAIL_COND_V(t.is_null(), nullptr);
-		String l = t->get_locale();
-
-		int score = compare_locales(p_locale, l);
-		if (score > 0 && score >= best_score) {
-			res = t;
-			best_score = score;
-			if (score == 10) {
-				break; // Exact match, skip the rest.
-			}
-		}
-	}
-	return res;
-}
-
-void TranslationServer::clear() {
-	translations.clear();
-}
-
-StringName TranslationServer::translate(const StringName &p_message, const StringName &p_context) const {
-	// Match given message against the translation catalog for the project locale.
-
-	if (!enabled) {
-		return p_message;
-	}
-
-	StringName res = _get_message_from_translations(p_message, p_context, locale, false);
-
-	if (!res && fallback.length() >= 2) {
-		res = _get_message_from_translations(p_message, p_context, fallback, false);
-	}
-
-	if (!res) {
-		return pseudolocalization_enabled ? pseudolocalize(p_message) : p_message;
-	}
-
-	return pseudolocalization_enabled ? pseudolocalize(res) : res;
-}
-
-StringName TranslationServer::translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context) const {
-	if (!enabled) {
-		if (p_n == 1) {
-			return p_message;
-		}
-		return p_message_plural;
-	}
-
-	StringName res = _get_message_from_translations(p_message, p_context, locale, true, p_message_plural, p_n);
-
-	if (!res && fallback.length() >= 2) {
-		res = _get_message_from_translations(p_message, p_context, fallback, true, p_message_plural, p_n);
-	}
-
-	if (!res) {
-		if (p_n == 1) {
-			return p_message;
-		}
-		return p_message_plural;
-	}
-
-	return res;
-}
-
-StringName TranslationServer::_get_message_from_translations(const StringName &p_message, const StringName &p_context, const String &p_locale, bool plural, const String &p_message_plural, int p_n) const {
-	StringName res;
-	int best_score = 0;
-
-	for (const Ref<Translation> &E : translations) {
-		const Ref<Translation> &t = E;
-		ERR_FAIL_COND_V(t.is_null(), p_message);
-		String l = t->get_locale();
-
-		int score = compare_locales(p_locale, l);
-		if (score > 0 && score >= best_score) {
-			StringName r;
-			if (!plural) {
-				r = t->get_message(p_message, p_context);
-			} else {
-				r = t->get_plural_message(p_message, p_message_plural, p_n, p_context);
-			}
-			if (!r) {
-				continue;
-			}
-			res = r;
-			best_score = score;
-			if (score == 10) {
-				break; // Exact match, skip the rest.
-			}
-		}
-	}
-
-	return res;
-}
-
-TranslationServer *TranslationServer::singleton = nullptr;
-
-bool TranslationServer::_load_translations(const String &p_from) {
-	if (ProjectSettings::get_singleton()->has_setting(p_from)) {
-		const Vector<String> &translation_names = GLOBAL_GET(p_from);
-
-		int tcount = translation_names.size();
-
-		if (tcount) {
-			const String *r = translation_names.ptr();
-
-			for (int i = 0; i < tcount; i++) {
-				Ref<Translation> tr = ResourceLoader::load(r[i]);
-				if (tr.is_valid()) {
-					add_translation(tr);
-				}
-			}
-		}
-		return true;
-	}
-
-	return false;
-}
-
-void TranslationServer::setup() {
-	String test = GLOBAL_DEF("internationalization/locale/test", "");
-	test = test.strip_edges();
-	if (!test.is_empty()) {
-		set_locale(test);
-	} else {
-		set_locale(OS::get_singleton()->get_locale());
-	}
-
-	fallback = GLOBAL_DEF("internationalization/locale/fallback", "en");
-	pseudolocalization_enabled = GLOBAL_DEF("internationalization/pseudolocalization/use_pseudolocalization", false);
-	pseudolocalization_accents_enabled = GLOBAL_DEF("internationalization/pseudolocalization/replace_with_accents", true);
-	pseudolocalization_double_vowels_enabled = GLOBAL_DEF("internationalization/pseudolocalization/double_vowels", false);
-	pseudolocalization_fake_bidi_enabled = GLOBAL_DEF("internationalization/pseudolocalization/fake_bidi", false);
-	pseudolocalization_override_enabled = GLOBAL_DEF("internationalization/pseudolocalization/override", false);
-	expansion_ratio = GLOBAL_DEF("internationalization/pseudolocalization/expansion_ratio", 0.0);
-	pseudolocalization_prefix = GLOBAL_DEF("internationalization/pseudolocalization/prefix", "[");
-	pseudolocalization_suffix = GLOBAL_DEF("internationalization/pseudolocalization/suffix", "]");
-	pseudolocalization_skip_placeholders_enabled = GLOBAL_DEF("internationalization/pseudolocalization/skip_placeholders", true);
-
-#ifdef TOOLS_ENABLED
-	ProjectSettings::get_singleton()->set_custom_property_info(PropertyInfo(Variant::STRING, "internationalization/locale/fallback", PROPERTY_HINT_LOCALE_ID, ""));
-#endif
-}
-
-void TranslationServer::set_tool_translation(const Ref<Translation> &p_translation) {
-	tool_translation = p_translation;
-}
-
-Ref<Translation> TranslationServer::get_tool_translation() const {
-	return tool_translation;
-}
-
-String TranslationServer::get_tool_locale() {
-#ifdef TOOLS_ENABLED
-	if (Engine::get_singleton()->is_editor_hint() || Engine::get_singleton()->is_project_manager_hint()) {
-		if (TranslationServer::get_singleton()->get_tool_translation().is_valid()) {
-			return tool_translation->get_locale();
-		} else {
-			return "en";
-		}
-	} else {
-#else
-	{
-#endif
-		// Look for best matching loaded translation.
-		String best_locale = "en";
-		int best_score = 0;
-
-		for (const Ref<Translation> &E : translations) {
-			const Ref<Translation> &t = E;
-			ERR_FAIL_COND_V(t.is_null(), best_locale);
-			String l = t->get_locale();
-
-			int score = compare_locales(locale, l);
-			if (score > 0 && score >= best_score) {
-				best_locale = l;
-				best_score = score;
-				if (score == 10) {
-					break; // Exact match, skip the rest.
-				}
-			}
-		}
-		return best_locale;
-	}
-}
-
-StringName TranslationServer::tool_translate(const StringName &p_message, const StringName &p_context) const {
-	if (tool_translation.is_valid()) {
-		StringName r = tool_translation->get_message(p_message, p_context);
-		if (r) {
-			return editor_pseudolocalization ? tool_pseudolocalize(r) : r;
-		}
-	}
-	return editor_pseudolocalization ? tool_pseudolocalize(p_message) : p_message;
-}
-
-StringName TranslationServer::tool_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context) const {
-	if (tool_translation.is_valid()) {
-		StringName r = tool_translation->get_plural_message(p_message, p_message_plural, p_n, p_context);
-		if (r) {
-			return r;
-		}
-	}
-
-	if (p_n == 1) {
-		return p_message;
-	}
-	return p_message_plural;
-}
-
-void TranslationServer::set_property_translation(const Ref<Translation> &p_translation) {
-	property_translation = p_translation;
-}
-
-StringName TranslationServer::property_translate(const StringName &p_message, const StringName &p_context) const {
-	if (property_translation.is_valid()) {
-		StringName r = property_translation->get_message(p_message, p_context);
-		if (r) {
-			return r;
-		}
-	}
-	return p_message;
-}
-
-void TranslationServer::set_doc_translation(const Ref<Translation> &p_translation) {
-	doc_translation = p_translation;
-}
-
-StringName TranslationServer::doc_translate(const StringName &p_message, const StringName &p_context) const {
-	if (doc_translation.is_valid()) {
-		StringName r = doc_translation->get_message(p_message, p_context);
-		if (r) {
-			return r;
-		}
-	}
-	return p_message;
-}
-
-StringName TranslationServer::doc_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context) const {
-	if (doc_translation.is_valid()) {
-		StringName r = doc_translation->get_plural_message(p_message, p_message_plural, p_n, p_context);
-		if (r) {
-			return r;
-		}
-	}
-
-	if (p_n == 1) {
-		return p_message;
-	}
-	return p_message_plural;
-}
-
-void TranslationServer::set_extractable_translation(const Ref<Translation> &p_translation) {
-	extractable_translation = p_translation;
-}
-
-StringName TranslationServer::extractable_translate(const StringName &p_message, const StringName &p_context) const {
-	if (extractable_translation.is_valid()) {
-		StringName r = extractable_translation->get_message(p_message, p_context);
-		if (r) {
-			return r;
-		}
-	}
-	return p_message;
-}
-
-StringName TranslationServer::extractable_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context) const {
-	if (extractable_translation.is_valid()) {
-		StringName r = extractable_translation->get_plural_message(p_message, p_message_plural, p_n, p_context);
-		if (r) {
-			return r;
-		}
-	}
-
-	if (p_n == 1) {
-		return p_message;
-	}
-	return p_message_plural;
-}
-
-bool TranslationServer::is_pseudolocalization_enabled() const {
-	return pseudolocalization_enabled;
-}
-
-void TranslationServer::set_pseudolocalization_enabled(bool p_enabled) {
-	pseudolocalization_enabled = p_enabled;
-
-	ResourceLoader::reload_translation_remaps();
-
-	if (OS::get_singleton()->get_main_loop()) {
-		OS::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_TRANSLATION_CHANGED);
-	}
-}
-
-void TranslationServer::set_editor_pseudolocalization(bool p_enabled) {
-	editor_pseudolocalization = p_enabled;
-}
-
-void TranslationServer::reload_pseudolocalization() {
-	pseudolocalization_accents_enabled = GLOBAL_GET("internationalization/pseudolocalization/replace_with_accents");
-	pseudolocalization_double_vowels_enabled = GLOBAL_GET("internationalization/pseudolocalization/double_vowels");
-	pseudolocalization_fake_bidi_enabled = GLOBAL_GET("internationalization/pseudolocalization/fake_bidi");
-	pseudolocalization_override_enabled = GLOBAL_GET("internationalization/pseudolocalization/override");
-	expansion_ratio = GLOBAL_GET("internationalization/pseudolocalization/expansion_ratio");
-	pseudolocalization_prefix = GLOBAL_GET("internationalization/pseudolocalization/prefix");
-	pseudolocalization_suffix = GLOBAL_GET("internationalization/pseudolocalization/suffix");
-	pseudolocalization_skip_placeholders_enabled = GLOBAL_GET("internationalization/pseudolocalization/skip_placeholders");
-
-	ResourceLoader::reload_translation_remaps();
-
-	if (OS::get_singleton()->get_main_loop()) {
-		OS::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_TRANSLATION_CHANGED);
-	}
-}
-
-StringName TranslationServer::pseudolocalize(const StringName &p_message) const {
-	String message = p_message;
-	int length = message.length();
-	if (pseudolocalization_override_enabled) {
-		message = get_override_string(message);
-	}
-
-	if (pseudolocalization_double_vowels_enabled) {
-		message = double_vowels(message);
-	}
-
-	if (pseudolocalization_accents_enabled) {
-		message = replace_with_accented_string(message);
-	}
-
-	if (pseudolocalization_fake_bidi_enabled) {
-		message = wrap_with_fakebidi_characters(message);
-	}
-
-	StringName res = add_padding(message, length);
-	return res;
-}
-
-StringName TranslationServer::tool_pseudolocalize(const StringName &p_message) const {
-	String message = p_message;
-	message = double_vowels(message);
-	message = replace_with_accented_string(message);
-	StringName res = "[!!! " + message + " !!!]";
-	return res;
-}
-
-String TranslationServer::get_override_string(String &p_message) const {
-	String res;
-	for (int i = 0; i < p_message.length(); i++) {
-		if (pseudolocalization_skip_placeholders_enabled && is_placeholder(p_message, i)) {
-			res += p_message[i];
-			res += p_message[i + 1];
-			i++;
-			continue;
-		}
-		res += '*';
-	}
-	return res;
-}
-
-String TranslationServer::double_vowels(String &p_message) const {
-	String res;
-	for (int i = 0; i < p_message.length(); i++) {
-		if (pseudolocalization_skip_placeholders_enabled && is_placeholder(p_message, i)) {
-			res += p_message[i];
-			res += p_message[i + 1];
-			i++;
-			continue;
-		}
-		res += p_message[i];
-		if (p_message[i] == 'a' || p_message[i] == 'e' || p_message[i] == 'i' || p_message[i] == 'o' || p_message[i] == 'u' ||
-				p_message[i] == 'A' || p_message[i] == 'E' || p_message[i] == 'I' || p_message[i] == 'O' || p_message[i] == 'U') {
-			res += p_message[i];
-		}
-	}
-	return res;
-};
-
-String TranslationServer::replace_with_accented_string(String &p_message) const {
-	String res;
-	for (int i = 0; i < p_message.length(); i++) {
-		if (pseudolocalization_skip_placeholders_enabled && is_placeholder(p_message, i)) {
-			res += p_message[i];
-			res += p_message[i + 1];
-			i++;
-			continue;
-		}
-		const char32_t *accented = get_accented_version(p_message[i]);
-		if (accented) {
-			res += accented;
-		} else {
-			res += p_message[i];
-		}
-	}
-	return res;
-}
-
-String TranslationServer::wrap_with_fakebidi_characters(String &p_message) const {
-	String res;
-	char32_t fakebidiprefix = U'\u202e';
-	char32_t fakebidisuffix = U'\u202c';
-	res += fakebidiprefix;
-	// The fake bidi unicode gets popped at every newline so pushing it back at every newline.
-	for (int i = 0; i < p_message.length(); i++) {
-		if (p_message[i] == '\n') {
-			res += fakebidisuffix;
-			res += p_message[i];
-			res += fakebidiprefix;
-		} else if (pseudolocalization_skip_placeholders_enabled && is_placeholder(p_message, i)) {
-			res += fakebidisuffix;
-			res += p_message[i];
-			res += p_message[i + 1];
-			res += fakebidiprefix;
-			i++;
-		} else {
-			res += p_message[i];
-		}
-	}
-	res += fakebidisuffix;
-	return res;
-}
-
-String TranslationServer::add_padding(const String &p_message, int p_length) const {
-	String underscores = String("_").repeat(p_length * expansion_ratio / 2);
-	String prefix = pseudolocalization_prefix + underscores;
-	String suffix = underscores + pseudolocalization_suffix;
-
-	return prefix + p_message + suffix;
-}
-
-const char32_t *TranslationServer::get_accented_version(char32_t p_character) const {
-	if (!is_ascii_alphabet_char(p_character)) {
-		return nullptr;
-	}
-
-	for (unsigned int i = 0; i < sizeof(_character_to_accented) / sizeof(_character_to_accented[0]); i++) {
-		if (_character_to_accented[i].character == p_character) {
-			return _character_to_accented[i].accented_character;
-		}
-	}
-
-	return nullptr;
-}
-
-bool TranslationServer::is_placeholder(String &p_message, int p_index) const {
-	return p_index < p_message.length() - 1 && p_message[p_index] == '%' &&
-			(p_message[p_index + 1] == 's' || p_message[p_index + 1] == 'c' || p_message[p_index + 1] == 'd' ||
-					p_message[p_index + 1] == 'o' || p_message[p_index + 1] == 'x' || p_message[p_index + 1] == 'X' || p_message[p_index + 1] == 'f');
-}
-
-#ifdef TOOLS_ENABLED
-void TranslationServer::get_argument_options(const StringName &p_function, int p_idx, List<String> *r_options) const {
-	const String pf = p_function;
-	if (p_idx == 0) {
-		HashMap<String, String> *target_hash_map = nullptr;
-		if (pf == "get_language_name") {
-			target_hash_map = &language_map;
-		} else if (pf == "get_script_name") {
-			target_hash_map = &script_map;
-		} else if (pf == "get_country_name") {
-			target_hash_map = &country_name_map;
-		}
-
-		if (target_hash_map) {
-			for (const KeyValue<String, String> &E : *target_hash_map) {
-				r_options->push_back(E.key.quote());
-			}
-		}
-	}
-	Object::get_argument_options(p_function, p_idx, r_options);
-}
-#endif // TOOLS_ENABLED
-
-void TranslationServer::_bind_methods() {
-	ClassDB::bind_method(D_METHOD("set_locale", "locale"), &TranslationServer::set_locale);
-	ClassDB::bind_method(D_METHOD("get_locale"), &TranslationServer::get_locale);
-	ClassDB::bind_method(D_METHOD("get_tool_locale"), &TranslationServer::get_tool_locale);
-
-	ClassDB::bind_method(D_METHOD("compare_locales", "locale_a", "locale_b"), &TranslationServer::compare_locales);
-	ClassDB::bind_method(D_METHOD("standardize_locale", "locale"), &TranslationServer::standardize_locale);
-
-	ClassDB::bind_method(D_METHOD("get_all_languages"), &TranslationServer::get_all_languages);
-	ClassDB::bind_method(D_METHOD("get_language_name", "language"), &TranslationServer::get_language_name);
-
-	ClassDB::bind_method(D_METHOD("get_all_scripts"), &TranslationServer::get_all_scripts);
-	ClassDB::bind_method(D_METHOD("get_script_name", "script"), &TranslationServer::get_script_name);
-
-	ClassDB::bind_method(D_METHOD("get_all_countries"), &TranslationServer::get_all_countries);
-	ClassDB::bind_method(D_METHOD("get_country_name", "country"), &TranslationServer::get_country_name);
-
-	ClassDB::bind_method(D_METHOD("get_locale_name", "locale"), &TranslationServer::get_locale_name);
-
-	ClassDB::bind_method(D_METHOD("translate", "message", "context"), &TranslationServer::translate, DEFVAL(StringName()));
-	ClassDB::bind_method(D_METHOD("translate_plural", "message", "plural_message", "n", "context"), &TranslationServer::translate_plural, DEFVAL(StringName()));
-
-	ClassDB::bind_method(D_METHOD("add_translation", "translation"), &TranslationServer::add_translation);
-	ClassDB::bind_method(D_METHOD("remove_translation", "translation"), &TranslationServer::remove_translation);
-	ClassDB::bind_method(D_METHOD("get_translation_object", "locale"), &TranslationServer::get_translation_object);
-
-	ClassDB::bind_method(D_METHOD("clear"), &TranslationServer::clear);
-
-	ClassDB::bind_method(D_METHOD("get_loaded_locales"), &TranslationServer::get_loaded_locales);
-
-	ClassDB::bind_method(D_METHOD("is_pseudolocalization_enabled"), &TranslationServer::is_pseudolocalization_enabled);
-	ClassDB::bind_method(D_METHOD("set_pseudolocalization_enabled", "enabled"), &TranslationServer::set_pseudolocalization_enabled);
-	ClassDB::bind_method(D_METHOD("reload_pseudolocalization"), &TranslationServer::reload_pseudolocalization);
-	ClassDB::bind_method(D_METHOD("pseudolocalize", "message"), &TranslationServer::pseudolocalize);
-	ADD_PROPERTY(PropertyInfo(Variant::Type::BOOL, "pseudolocalization_enabled"), "set_pseudolocalization_enabled", "is_pseudolocalization_enabled");
-}
-
-void TranslationServer::load_translations() {
-	_load_translations("internationalization/locale/translations"); //all
-	_load_translations("internationalization/locale/translations_" + locale.substr(0, 2));
-
-	if (locale.substr(0, 2) != locale) {
-		_load_translations("internationalization/locale/translations_" + locale);
-	}
-}
-
-TranslationServer::TranslationServer() {
-	singleton = this;
-	init_locale_info();
-}
diff --git a/core/string/translation.h b/core/string/translation.h
index 78d6721347..2c5baae8b7 100644
--- a/core/string/translation.h
+++ b/core/string/translation.h
@@ -74,134 +74,4 @@ public:
 	Translation() {}
 };
 
-class TranslationServer : public Object {
-	GDCLASS(TranslationServer, Object);
-
-	String locale = "en";
-	String fallback;
-
-	HashSet<Ref<Translation>> translations;
-	Ref<Translation> tool_translation;
-	Ref<Translation> property_translation;
-	Ref<Translation> doc_translation;
-	Ref<Translation> extractable_translation;
-
-	bool enabled = true;
-
-	bool pseudolocalization_enabled = false;
-	bool pseudolocalization_accents_enabled = false;
-	bool pseudolocalization_double_vowels_enabled = false;
-	bool pseudolocalization_fake_bidi_enabled = false;
-	bool pseudolocalization_override_enabled = false;
-	bool pseudolocalization_skip_placeholders_enabled = false;
-	bool editor_pseudolocalization = false;
-	float expansion_ratio = 0.0;
-	String pseudolocalization_prefix;
-	String pseudolocalization_suffix;
-
-	StringName tool_pseudolocalize(const StringName &p_message) const;
-	String get_override_string(String &p_message) const;
-	String double_vowels(String &p_message) const;
-	String replace_with_accented_string(String &p_message) const;
-	String wrap_with_fakebidi_characters(String &p_message) const;
-	String add_padding(const String &p_message, int p_length) const;
-	const char32_t *get_accented_version(char32_t p_character) const;
-	bool is_placeholder(String &p_message, int p_index) const;
-
-	static TranslationServer *singleton;
-	bool _load_translations(const String &p_from);
-	String _standardize_locale(const String &p_locale, bool p_add_defaults) const;
-
-	StringName _get_message_from_translations(const StringName &p_message, const StringName &p_context, const String &p_locale, bool plural, const String &p_message_plural = "", int p_n = 0) const;
-
-	static void _bind_methods();
-
-#ifndef DISABLE_DEPRECATED
-	static void _bind_compatibility_methods();
-#endif
-
-	struct LocaleScriptInfo {
-		String name;
-		String script;
-		String default_country;
-		HashSet<String> supported_countries;
-	};
-	static Vector<LocaleScriptInfo> locale_script_info;
-
-	static HashMap<String, String> language_map;
-	static HashMap<String, String> script_map;
-	static HashMap<String, String> locale_rename_map;
-	static HashMap<String, String> country_name_map;
-	static HashMap<String, String> country_rename_map;
-	static HashMap<String, String> variant_map;
-
-	void init_locale_info();
-
-public:
-	_FORCE_INLINE_ static TranslationServer *get_singleton() { return singleton; }
-
-	void set_enabled(bool p_enabled) { enabled = p_enabled; }
-	_FORCE_INLINE_ bool is_enabled() const { return enabled; }
-
-	void set_locale(const String &p_locale);
-	String get_locale() const;
-	Ref<Translation> get_translation_object(const String &p_locale);
-
-	Vector<String> get_all_languages() const;
-	String get_language_name(const String &p_language) const;
-
-	Vector<String> get_all_scripts() const;
-	String get_script_name(const String &p_script) const;
-
-	Vector<String> get_all_countries() const;
-	String get_country_name(const String &p_country) const;
-
-	String get_locale_name(const String &p_locale) const;
-
-	PackedStringArray get_loaded_locales() const;
-
-	void add_translation(const Ref<Translation> &p_translation);
-	void remove_translation(const Ref<Translation> &p_translation);
-
-	StringName translate(const StringName &p_message, const StringName &p_context = "") const;
-	StringName translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context = "") const;
-
-	StringName pseudolocalize(const StringName &p_message) const;
-
-	bool is_pseudolocalization_enabled() const;
-	void set_pseudolocalization_enabled(bool p_enabled);
-	void set_editor_pseudolocalization(bool p_enabled);
-	void reload_pseudolocalization();
-
-	String standardize_locale(const String &p_locale) const;
-
-	int compare_locales(const String &p_locale_a, const String &p_locale_b) const;
-
-	String get_tool_locale();
-	void set_tool_translation(const Ref<Translation> &p_translation);
-	Ref<Translation> get_tool_translation() const;
-	StringName tool_translate(const StringName &p_message, const StringName &p_context = "") const;
-	StringName tool_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context = "") const;
-	void set_property_translation(const Ref<Translation> &p_translation);
-	StringName property_translate(const StringName &p_message, const StringName &p_context = "") const;
-	void set_doc_translation(const Ref<Translation> &p_translation);
-	StringName doc_translate(const StringName &p_message, const StringName &p_context = "") const;
-	StringName doc_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context = "") const;
-	void set_extractable_translation(const Ref<Translation> &p_translation);
-	StringName extractable_translate(const StringName &p_message, const StringName &p_context = "") const;
-	StringName extractable_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context = "") const;
-
-	void setup();
-
-	void clear();
-
-	void load_translations();
-
-#ifdef TOOLS_ENABLED
-	virtual void get_argument_options(const StringName &p_function, int p_idx, List<String> *r_options) const override;
-#endif // TOOLS_ENABLED
-
-	TranslationServer();
-};
-
 #endif // TRANSLATION_H
diff --git a/core/string/translation_po.cpp b/core/string/translation_po.cpp
index 06fd4717d7..8e275505b0 100644
--- a/core/string/translation_po.cpp
+++ b/core/string/translation_po.cpp
@@ -140,43 +140,87 @@ int TranslationPO::_get_plural_index(int p_n) const {
 	input_val.clear();
 	input_val.push_back(p_n);
 
-	Variant result;
-	for (int i = 0; i < equi_tests.size(); i++) {
-		Error err = expr->parse(equi_tests[i], input_name);
-		ERR_FAIL_COND_V_MSG(err != OK, 0, "Cannot parse expression. Error: " + expr->get_error_text());
+	return _eq_test(equi_tests, 0);
+}
 
-		result = expr->execute(input_val);
-		ERR_FAIL_COND_V_MSG(expr->has_execute_failed(), 0, "Cannot evaluate expression.");
+int TranslationPO::_eq_test(const Ref<EQNode> &p_node, const Variant &p_result) const {
+	if (p_node.is_valid()) {
+		Error err = expr->parse(p_node->regex, input_name);
+		ERR_FAIL_COND_V_MSG(err != OK, 0, vformat("Cannot parse expression \"%s\". Error: %s", p_node->regex, expr->get_error_text()));
 
-		// Last expression. Variant result will either map to a bool or an integer, in both cases returning it will give the correct plural index.
-		if (i + 1 == equi_tests.size()) {
-			return result;
-		}
+		Variant result = expr->execute(input_val);
+		ERR_FAIL_COND_V_MSG(expr->has_execute_failed(), 0, vformat("Cannot evaluate expression \"%s\".", p_node->regex));
 
 		if (bool(result)) {
-			return i;
+			return _eq_test(p_node->left, result);
+		} else {
+			return _eq_test(p_node->right, result);
 		}
+	} else {
+		return p_result;
+	}
+}
+
+int TranslationPO::_find_unquoted(const String &p_src, char32_t p_chr) const {
+	const int len = p_src.length();
+	if (len == 0) {
+		return -1;
 	}
 
-	ERR_FAIL_V_MSG(0, "Unexpected. Function should have returned. Please report this bug.");
+	const char32_t *src = p_src.get_data();
+	bool in_quote = false;
+	for (int i = 0; i < len; i++) {
+		if (in_quote) {
+			if (src[i] == ')') {
+				in_quote = false;
+			}
+		} else {
+			if (src[i] == '(') {
+				in_quote = true;
+			} else if (src[i] == p_chr) {
+				return i;
+			}
+		}
+	}
+
+	return -1;
 }
 
-void TranslationPO::_cache_plural_tests(const String &p_plural_rule) {
+void TranslationPO::_cache_plural_tests(const String &p_plural_rule, Ref<EQNode> &p_node) {
 	// Some examples of p_plural_rule passed in can have the form:
 	// "n==0 ? 0 : n==1 ? 1 : n==2 ? 2 : n%100>=3 && n%100<=10 ? 3 : n%100>=11 && n%100<=99 ? 4 : 5" (Arabic)
 	// "n >= 2" (French) // When evaluating the last, especially careful with this one.
 	// "n != 1" (English)
-	int first_ques_mark = p_plural_rule.find("?");
+
+	String rule = p_plural_rule;
+	if (rule.begins_with("(") && rule.ends_with(")")) {
+		int bcount = 0;
+		for (int i = 1; i < rule.length() - 1 && bcount >= 0; i++) {
+			if (rule[i] == '(') {
+				bcount++;
+			} else if (rule[i] == ')') {
+				bcount--;
+			}
+		}
+		if (bcount == 0) {
+			rule = rule.substr(1, rule.length() - 2);
+		}
+	}
+
+	int first_ques_mark = _find_unquoted(rule, '?');
+	int first_colon = _find_unquoted(rule, ':');
+
 	if (first_ques_mark == -1) {
-		equi_tests.push_back(p_plural_rule.strip_edges());
+		p_node->regex = rule.strip_edges();
 		return;
 	}
 
-	String equi_test = p_plural_rule.substr(0, first_ques_mark).strip_edges();
-	equi_tests.push_back(equi_test);
+	p_node->regex = rule.substr(0, first_ques_mark).strip_edges();
 
-	String after_colon = p_plural_rule.substr(p_plural_rule.find(":") + 1, p_plural_rule.length());
-	_cache_plural_tests(after_colon);
+	p_node->left.instantiate();
+	_cache_plural_tests(rule.substr(first_ques_mark + 1, first_colon - first_ques_mark - 1).strip_edges(), p_node->left);
+	p_node->right.instantiate();
+	_cache_plural_tests(rule.substr(first_colon + 1).strip_edges(), p_node->right);
 }
 
 void TranslationPO::set_plural_rule(const String &p_plural_rule) {
@@ -188,12 +232,12 @@ void TranslationPO::set_plural_rule(const String &p_plural_rule) {
 
 	int expression_start = p_plural_rule.find("=", first_semi_col) + 1;
 	int second_semi_col = p_plural_rule.rfind(";");
-	plural_rule = p_plural_rule.substr(expression_start, second_semi_col - expression_start);
+	plural_rule = p_plural_rule.substr(expression_start, second_semi_col - expression_start).strip_edges();
 
 	// Setup the cache to make evaluating plural rule faster later on.
-	plural_rule = plural_rule.replacen("(", "");
-	plural_rule = plural_rule.replacen(")", "");
-	_cache_plural_tests(plural_rule);
+	equi_tests.instantiate();
+	_cache_plural_tests(plural_rule, equi_tests);
+
 	expr.instantiate();
 	input_name.push_back("n");
 }
diff --git a/core/string/translation_po.h b/core/string/translation_po.h
index 73f9b33a87..ba820c6ee4 100644
--- a/core/string/translation_po.h
+++ b/core/string/translation_po.h
@@ -50,7 +50,17 @@ class TranslationPO : public Translation {
 	String plural_rule;
 
 	// Cache temporary variables related to _get_plural_index() to make it faster
-	Vector<String> equi_tests;
+	class EQNode : public RefCounted {
+	public:
+		String regex;
+		Ref<EQNode> left;
+		Ref<EQNode> right;
+	};
+	Ref<EQNode> equi_tests;
+
+	int _find_unquoted(const String &p_src, char32_t p_chr) const;
+	int _eq_test(const Ref<EQNode> &p_node, const Variant &p_result) const;
+
 	Vector<String> input_name;
 	mutable Ref<Expression> expr;
 	mutable Array input_val;
@@ -59,7 +69,7 @@ class TranslationPO : public Translation {
 	mutable int last_plural_n = -1; // Set it to an impossible value at the beginning.
 	mutable int last_plural_mapped_index = 0;
 
-	void _cache_plural_tests(const String &p_plural_rule);
+	void _cache_plural_tests(const String &p_plural_rule, Ref<EQNode> &p_node);
 	int _get_plural_index(int p_n) const;
 
 	Vector<String> _get_message_list() const override;
diff --git a/core/string/translation_server.compat.inc b/core/string/translation_server.compat.inc
new file mode 100644
index 0000000000..9d1ee8b9df
--- /dev/null
+++ b/core/string/translation_server.compat.inc
@@ -0,0 +1,38 @@
+/**************************************************************************/
+/*  translation_server.compat.inc                                         */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* Permission is hereby granted, free of charge, to any person obtaining  */
+/* a copy of this software and associated documentation files (the        */
+/* "Software"), to deal in the Software without restriction, including    */
+/* without limitation the rights to use, copy, modify, merge, publish,    */
+/* distribute, sublicense, and/or sell copies of the Software, and to     */
+/* permit persons to whom the Software is furnished to do so, subject to  */
+/* the following conditions:                                              */
+/*                                                                        */
+/* The above copyright notice and this permission notice shall be         */
+/* included in all copies or substantial portions of the Software.        */
+/*                                                                        */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF     */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY   */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,   */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
+/**************************************************************************/
+
+#ifndef DISABLE_DEPRECATED
+
+void TranslationServer::_bind_compatibility_methods() {
+	ClassDB::bind_compatibility_method(D_METHOD("translate", "message", "context"), &TranslationServer::translate, DEFVAL(""));
+	ClassDB::bind_compatibility_method(D_METHOD("translate_plural", "message", "plural_message", "n", "context"), &TranslationServer::translate_plural, DEFVAL(""));
+}
+
+#endif
diff --git a/core/string/translation_server.cpp b/core/string/translation_server.cpp
new file mode 100644
index 0000000000..6e784881d0
--- /dev/null
+++ b/core/string/translation_server.cpp
@@ -0,0 +1,947 @@
+/**************************************************************************/
+/*  translation_server.cpp                                                */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* Permission is hereby granted, free of charge, to any person obtaining  */
+/* a copy of this software and associated documentation files (the        */
+/* "Software"), to deal in the Software without restriction, including    */
+/* without limitation the rights to use, copy, modify, merge, publish,    */
+/* distribute, sublicense, and/or sell copies of the Software, and to     */
+/* permit persons to whom the Software is furnished to do so, subject to  */
+/* the following conditions:                                              */
+/*                                                                        */
+/* The above copyright notice and this permission notice shall be         */
+/* included in all copies or substantial portions of the Software.        */
+/*                                                                        */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF     */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY   */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,   */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
+/**************************************************************************/
+
+#include "translation_server.h"
+#include "translation_server.compat.inc"
+
+#include "core/config/project_settings.h"
+#include "core/io/resource_loader.h"
+#include "core/os/os.h"
+#include "core/string/locales.h"
+
+#ifdef TOOLS_ENABLED
+#include "main/main.h"
+#endif
+
+struct _character_accent_pair {
+	const char32_t character;
+	const char32_t *accented_character;
+};
+
+static _character_accent_pair _character_to_accented[] = {
+	{ 'A', U"Å" },
+	{ 'B', U"ß" },
+	{ 'C', U"Ç" },
+	{ 'D', U"Ð" },
+	{ 'E', U"É" },
+	{ 'F', U"F́" },
+	{ 'G', U"Ĝ" },
+	{ 'H', U"Ĥ" },
+	{ 'I', U"Ĩ" },
+	{ 'J', U"Ĵ" },
+	{ 'K', U"ĸ" },
+	{ 'L', U"Ł" },
+	{ 'M', U"Ḿ" },
+	{ 'N', U"й" },
+	{ 'O', U"Ö" },
+	{ 'P', U"Ṕ" },
+	{ 'Q', U"Q́" },
+	{ 'R', U"Ř" },
+	{ 'S', U"Ŝ" },
+	{ 'T', U"Ŧ" },
+	{ 'U', U"Ũ" },
+	{ 'V', U"Ṽ" },
+	{ 'W', U"Ŵ" },
+	{ 'X', U"X́" },
+	{ 'Y', U"Ÿ" },
+	{ 'Z', U"Ž" },
+	{ 'a', U"á" },
+	{ 'b', U"ḅ" },
+	{ 'c', U"ć" },
+	{ 'd', U"d́" },
+	{ 'e', U"é" },
+	{ 'f', U"f́" },
+	{ 'g', U"ǵ" },
+	{ 'h', U"h̀" },
+	{ 'i', U"í" },
+	{ 'j', U"ǰ" },
+	{ 'k', U"ḱ" },
+	{ 'l', U"ł" },
+	{ 'm', U"m̀" },
+	{ 'n', U"ή" },
+	{ 'o', U"ô" },
+	{ 'p', U"ṕ" },
+	{ 'q', U"q́" },
+	{ 'r', U"ŕ" },
+	{ 's', U"š" },
+	{ 't', U"ŧ" },
+	{ 'u', U"ü" },
+	{ 'v', U"ṽ" },
+	{ 'w', U"ŵ" },
+	{ 'x', U"x́" },
+	{ 'y', U"ý" },
+	{ 'z', U"ź" },
+};
+
+Vector<TranslationServer::LocaleScriptInfo> TranslationServer::locale_script_info;
+
+HashMap<String, String> TranslationServer::language_map;
+HashMap<String, String> TranslationServer::script_map;
+HashMap<String, String> TranslationServer::locale_rename_map;
+HashMap<String, String> TranslationServer::country_name_map;
+HashMap<String, String> TranslationServer::variant_map;
+HashMap<String, String> TranslationServer::country_rename_map;
+
+void TranslationServer::init_locale_info() {
+	// Init locale info.
+	language_map.clear();
+	int idx = 0;
+	while (language_list[idx][0] != nullptr) {
+		language_map[language_list[idx][0]] = String::utf8(language_list[idx][1]);
+		idx++;
+	}
+
+	// Init locale-script map.
+	locale_script_info.clear();
+	idx = 0;
+	while (locale_scripts[idx][0] != nullptr) {
+		LocaleScriptInfo info;
+		info.name = locale_scripts[idx][0];
+		info.script = locale_scripts[idx][1];
+		info.default_country = locale_scripts[idx][2];
+		Vector<String> supported_countries = String(locale_scripts[idx][3]).split(",", false);
+		for (int i = 0; i < supported_countries.size(); i++) {
+			info.supported_countries.insert(supported_countries[i]);
+		}
+		locale_script_info.push_back(info);
+		idx++;
+	}
+
+	// Init supported script list.
+	script_map.clear();
+	idx = 0;
+	while (script_list[idx][0] != nullptr) {
+		script_map[script_list[idx][1]] = String::utf8(script_list[idx][0]);
+		idx++;
+	}
+
+	// Init regional variant map.
+	variant_map.clear();
+	idx = 0;
+	while (locale_variants[idx][0] != nullptr) {
+		variant_map[locale_variants[idx][0]] = locale_variants[idx][1];
+		idx++;
+	}
+
+	// Init locale renames.
+	locale_rename_map.clear();
+	idx = 0;
+	while (locale_renames[idx][0] != nullptr) {
+		if (!String(locale_renames[idx][1]).is_empty()) {
+			locale_rename_map[locale_renames[idx][0]] = locale_renames[idx][1];
+		}
+		idx++;
+	}
+
+	// Init country names.
+	country_name_map.clear();
+	idx = 0;
+	while (country_names[idx][0] != nullptr) {
+		country_name_map[String(country_names[idx][0])] = String::utf8(country_names[idx][1]);
+		idx++;
+	}
+
+	// Init country renames.
+	country_rename_map.clear();
+	idx = 0;
+	while (country_renames[idx][0] != nullptr) {
+		if (!String(country_renames[idx][1]).is_empty()) {
+			country_rename_map[country_renames[idx][0]] = country_renames[idx][1];
+		}
+		idx++;
+	}
+}
+
+String TranslationServer::standardize_locale(const String &p_locale) const {
+	return _standardize_locale(p_locale, false);
+}
+
+String TranslationServer::_standardize_locale(const String &p_locale, bool p_add_defaults) const {
+	// Replaces '-' with '_' for macOS style locales.
+	String univ_locale = p_locale.replace("-", "_");
+
+	// Extract locale elements.
+	String lang_name, script_name, country_name, variant_name;
+	Vector<String> locale_elements = univ_locale.get_slice("@", 0).split("_");
+	lang_name = locale_elements[0];
+	if (locale_elements.size() >= 2) {
+		if (locale_elements[1].length() == 4 && is_ascii_upper_case(locale_elements[1][0]) && is_ascii_lower_case(locale_elements[1][1]) && is_ascii_lower_case(locale_elements[1][2]) && is_ascii_lower_case(locale_elements[1][3])) {
+			script_name = locale_elements[1];
+		}
+		if (locale_elements[1].length() == 2 && is_ascii_upper_case(locale_elements[1][0]) && is_ascii_upper_case(locale_elements[1][1])) {
+			country_name = locale_elements[1];
+		}
+	}
+	if (locale_elements.size() >= 3) {
+		if (locale_elements[2].length() == 2 && is_ascii_upper_case(locale_elements[2][0]) && is_ascii_upper_case(locale_elements[2][1])) {
+			country_name = locale_elements[2];
+		} else if (variant_map.has(locale_elements[2].to_lower()) && variant_map[locale_elements[2].to_lower()] == lang_name) {
+			variant_name = locale_elements[2].to_lower();
+		}
+	}
+	if (locale_elements.size() >= 4) {
+		if (variant_map.has(locale_elements[3].to_lower()) && variant_map[locale_elements[3].to_lower()] == lang_name) {
+			variant_name = locale_elements[3].to_lower();
+		}
+	}
+
+	// Try extract script and variant from the extra part.
+	Vector<String> script_extra = univ_locale.get_slice("@", 1).split(";");
+	for (int i = 0; i < script_extra.size(); i++) {
+		if (script_extra[i].to_lower() == "cyrillic") {
+			script_name = "Cyrl";
+			break;
+		} else if (script_extra[i].to_lower() == "latin") {
+			script_name = "Latn";
+			break;
+		} else if (script_extra[i].to_lower() == "devanagari") {
+			script_name = "Deva";
+			break;
+		} else if (variant_map.has(script_extra[i].to_lower()) && variant_map[script_extra[i].to_lower()] == lang_name) {
+			variant_name = script_extra[i].to_lower();
+		}
+	}
+
+	// Handles known non-ISO language names used e.g. on Windows.
+	if (locale_rename_map.has(lang_name)) {
+		lang_name = locale_rename_map[lang_name];
+	}
+
+	// Handle country renames.
+	if (country_rename_map.has(country_name)) {
+		country_name = country_rename_map[country_name];
+	}
+
+	// Remove unsupported script codes.
+	if (!script_map.has(script_name)) {
+		script_name = "";
+	}
+
+	// Add script code base on language and country codes for some ambiguous cases.
+	if (p_add_defaults) {
+		if (script_name.is_empty()) {
+			for (int i = 0; i < locale_script_info.size(); i++) {
+				const LocaleScriptInfo &info = locale_script_info[i];
+				if (info.name == lang_name) {
+					if (country_name.is_empty() || info.supported_countries.has(country_name)) {
+						script_name = info.script;
+						break;
+					}
+				}
+			}
+		}
+		if (!script_name.is_empty() && country_name.is_empty()) {
+			// Add conntry code based on script for some ambiguous cases.
+			for (int i = 0; i < locale_script_info.size(); i++) {
+				const LocaleScriptInfo &info = locale_script_info[i];
+				if (info.name == lang_name && info.script == script_name) {
+					country_name = info.default_country;
+					break;
+				}
+			}
+		}
+	}
+
+	// Combine results.
+	String out = lang_name;
+	if (!script_name.is_empty()) {
+		out = out + "_" + script_name;
+	}
+	if (!country_name.is_empty()) {
+		out = out + "_" + country_name;
+	}
+	if (!variant_name.is_empty()) {
+		out = out + "_" + variant_name;
+	}
+	return out;
+}
+
+int TranslationServer::compare_locales(const String &p_locale_a, const String &p_locale_b) const {
+	String locale_a = _standardize_locale(p_locale_a, true);
+	String locale_b = _standardize_locale(p_locale_b, true);
+
+	if (locale_a == locale_b) {
+		// Exact match.
+		return 10;
+	}
+
+	Vector<String> locale_a_elements = locale_a.split("_");
+	Vector<String> locale_b_elements = locale_b.split("_");
+	if (locale_a_elements[0] == locale_b_elements[0]) {
+		// Matching language, both locales have extra parts.
+		// Return number of matching elements.
+		int matching_elements = 1;
+		for (int i = 1; i < locale_a_elements.size(); i++) {
+			for (int j = 1; j < locale_b_elements.size(); j++) {
+				if (locale_a_elements[i] == locale_b_elements[j]) {
+					matching_elements++;
+				}
+			}
+		}
+		return matching_elements;
+	} else {
+		// No match.
+		return 0;
+	}
+}
+
+String TranslationServer::get_locale_name(const String &p_locale) const {
+	String lang_name, script_name, country_name;
+	Vector<String> locale_elements = standardize_locale(p_locale).split("_");
+	lang_name = locale_elements[0];
+	if (locale_elements.size() >= 2) {
+		if (locale_elements[1].length() == 4 && is_ascii_upper_case(locale_elements[1][0]) && is_ascii_lower_case(locale_elements[1][1]) && is_ascii_lower_case(locale_elements[1][2]) && is_ascii_lower_case(locale_elements[1][3])) {
+			script_name = locale_elements[1];
+		}
+		if (locale_elements[1].length() == 2 && is_ascii_upper_case(locale_elements[1][0]) && is_ascii_upper_case(locale_elements[1][1])) {
+			country_name = locale_elements[1];
+		}
+	}
+	if (locale_elements.size() >= 3) {
+		if (locale_elements[2].length() == 2 && is_ascii_upper_case(locale_elements[2][0]) && is_ascii_upper_case(locale_elements[2][1])) {
+			country_name = locale_elements[2];
+		}
+	}
+
+	String name = language_map[lang_name];
+	if (!script_name.is_empty()) {
+		name = name + " (" + script_map[script_name] + ")";
+	}
+	if (!country_name.is_empty()) {
+		name = name + ", " + country_name_map[country_name];
+	}
+	return name;
+}
+
+Vector<String> TranslationServer::get_all_languages() const {
+	Vector<String> languages;
+
+	for (const KeyValue<String, String> &E : language_map) {
+		languages.push_back(E.key);
+	}
+
+	return languages;
+}
+
+String TranslationServer::get_language_name(const String &p_language) const {
+	return language_map[p_language];
+}
+
+Vector<String> TranslationServer::get_all_scripts() const {
+	Vector<String> scripts;
+
+	for (const KeyValue<String, String> &E : script_map) {
+		scripts.push_back(E.key);
+	}
+
+	return scripts;
+}
+
+String TranslationServer::get_script_name(const String &p_script) const {
+	return script_map[p_script];
+}
+
+Vector<String> TranslationServer::get_all_countries() const {
+	Vector<String> countries;
+
+	for (const KeyValue<String, String> &E : country_name_map) {
+		countries.push_back(E.key);
+	}
+
+	return countries;
+}
+
+String TranslationServer::get_country_name(const String &p_country) const {
+	return country_name_map[p_country];
+}
+
+void TranslationServer::set_locale(const String &p_locale) {
+	String new_locale = standardize_locale(p_locale);
+	if (locale == new_locale) {
+		return;
+	}
+
+	locale = new_locale;
+	ResourceLoader::reload_translation_remaps();
+
+	if (OS::get_singleton()->get_main_loop()) {
+		OS::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_TRANSLATION_CHANGED);
+	}
+}
+
+String TranslationServer::get_locale() const {
+	return locale;
+}
+
+PackedStringArray TranslationServer::get_loaded_locales() const {
+	PackedStringArray locales;
+	for (const Ref<Translation> &E : translations) {
+		const Ref<Translation> &t = E;
+		ERR_FAIL_COND_V(t.is_null(), PackedStringArray());
+		String l = t->get_locale();
+
+		locales.push_back(l);
+	}
+
+	return locales;
+}
+
+void TranslationServer::add_translation(const Ref<Translation> &p_translation) {
+	translations.insert(p_translation);
+}
+
+void TranslationServer::remove_translation(const Ref<Translation> &p_translation) {
+	translations.erase(p_translation);
+}
+
+Ref<Translation> TranslationServer::get_translation_object(const String &p_locale) {
+	Ref<Translation> res;
+	int best_score = 0;
+
+	for (const Ref<Translation> &E : translations) {
+		const Ref<Translation> &t = E;
+		ERR_FAIL_COND_V(t.is_null(), nullptr);
+		String l = t->get_locale();
+
+		int score = compare_locales(p_locale, l);
+		if (score > 0 && score >= best_score) {
+			res = t;
+			best_score = score;
+			if (score == 10) {
+				break; // Exact match, skip the rest.
+			}
+		}
+	}
+	return res;
+}
+
+void TranslationServer::clear() {
+	translations.clear();
+}
+
+StringName TranslationServer::translate(const StringName &p_message, const StringName &p_context) const {
+	// Match given message against the translation catalog for the project locale.
+
+	if (!enabled) {
+		return p_message;
+	}
+
+	StringName res = _get_message_from_translations(p_message, p_context, locale, false);
+
+	if (!res && fallback.length() >= 2) {
+		res = _get_message_from_translations(p_message, p_context, fallback, false);
+	}
+
+	if (!res) {
+		return pseudolocalization_enabled ? pseudolocalize(p_message) : p_message;
+	}
+
+	return pseudolocalization_enabled ? pseudolocalize(res) : res;
+}
+
+StringName TranslationServer::translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context) const {
+	if (!enabled) {
+		if (p_n == 1) {
+			return p_message;
+		}
+		return p_message_plural;
+	}
+
+	StringName res = _get_message_from_translations(p_message, p_context, locale, true, p_message_plural, p_n);
+
+	if (!res && fallback.length() >= 2) {
+		res = _get_message_from_translations(p_message, p_context, fallback, true, p_message_plural, p_n);
+	}
+
+	if (!res) {
+		if (p_n == 1) {
+			return p_message;
+		}
+		return p_message_plural;
+	}
+
+	return res;
+}
+
+StringName TranslationServer::_get_message_from_translations(const StringName &p_message, const StringName &p_context, const String &p_locale, bool plural, const String &p_message_plural, int p_n) const {
+	StringName res;
+	int best_score = 0;
+
+	for (const Ref<Translation> &E : translations) {
+		const Ref<Translation> &t = E;
+		ERR_FAIL_COND_V(t.is_null(), p_message);
+		String l = t->get_locale();
+
+		int score = compare_locales(p_locale, l);
+		if (score > 0 && score >= best_score) {
+			StringName r;
+			if (!plural) {
+				r = t->get_message(p_message, p_context);
+			} else {
+				r = t->get_plural_message(p_message, p_message_plural, p_n, p_context);
+			}
+			if (!r) {
+				continue;
+			}
+			res = r;
+			best_score = score;
+			if (score == 10) {
+				break; // Exact match, skip the rest.
+			}
+		}
+	}
+
+	return res;
+}
+
+TranslationServer *TranslationServer::singleton = nullptr;
+
+bool TranslationServer::_load_translations(const String &p_from) {
+	if (ProjectSettings::get_singleton()->has_setting(p_from)) {
+		const Vector<String> &translation_names = GLOBAL_GET(p_from);
+
+		int tcount = translation_names.size();
+
+		if (tcount) {
+			const String *r = translation_names.ptr();
+
+			for (int i = 0; i < tcount; i++) {
+				Ref<Translation> tr = ResourceLoader::load(r[i]);
+				if (tr.is_valid()) {
+					add_translation(tr);
+				}
+			}
+		}
+		return true;
+	}
+
+	return false;
+}
+
+void TranslationServer::setup() {
+	String test = GLOBAL_DEF("internationalization/locale/test", "");
+	test = test.strip_edges();
+	if (!test.is_empty()) {
+		set_locale(test);
+	} else {
+		set_locale(OS::get_singleton()->get_locale());
+	}
+
+	fallback = GLOBAL_DEF("internationalization/locale/fallback", "en");
+	pseudolocalization_enabled = GLOBAL_DEF("internationalization/pseudolocalization/use_pseudolocalization", false);
+	pseudolocalization_accents_enabled = GLOBAL_DEF("internationalization/pseudolocalization/replace_with_accents", true);
+	pseudolocalization_double_vowels_enabled = GLOBAL_DEF("internationalization/pseudolocalization/double_vowels", false);
+	pseudolocalization_fake_bidi_enabled = GLOBAL_DEF("internationalization/pseudolocalization/fake_bidi", false);
+	pseudolocalization_override_enabled = GLOBAL_DEF("internationalization/pseudolocalization/override", false);
+	expansion_ratio = GLOBAL_DEF("internationalization/pseudolocalization/expansion_ratio", 0.0);
+	pseudolocalization_prefix = GLOBAL_DEF("internationalization/pseudolocalization/prefix", "[");
+	pseudolocalization_suffix = GLOBAL_DEF("internationalization/pseudolocalization/suffix", "]");
+	pseudolocalization_skip_placeholders_enabled = GLOBAL_DEF("internationalization/pseudolocalization/skip_placeholders", true);
+
+#ifdef TOOLS_ENABLED
+	ProjectSettings::get_singleton()->set_custom_property_info(PropertyInfo(Variant::STRING, "internationalization/locale/fallback", PROPERTY_HINT_LOCALE_ID, ""));
+#endif
+}
+
+void TranslationServer::set_tool_translation(const Ref<Translation> &p_translation) {
+	tool_translation = p_translation;
+}
+
+Ref<Translation> TranslationServer::get_tool_translation() const {
+	return tool_translation;
+}
+
+String TranslationServer::get_tool_locale() {
+#ifdef TOOLS_ENABLED
+	if (Engine::get_singleton()->is_editor_hint() || Engine::get_singleton()->is_project_manager_hint()) {
+		if (TranslationServer::get_singleton()->get_tool_translation().is_valid()) {
+			return tool_translation->get_locale();
+		} else {
+			return "en";
+		}
+	} else {
+#else
+	{
+#endif
+		// Look for best matching loaded translation.
+		String best_locale = "en";
+		int best_score = 0;
+
+		for (const Ref<Translation> &E : translations) {
+			const Ref<Translation> &t = E;
+			ERR_FAIL_COND_V(t.is_null(), best_locale);
+			String l = t->get_locale();
+
+			int score = compare_locales(locale, l);
+			if (score > 0 && score >= best_score) {
+				best_locale = l;
+				best_score = score;
+				if (score == 10) {
+					break; // Exact match, skip the rest.
+				}
+			}
+		}
+		return best_locale;
+	}
+}
+
+StringName TranslationServer::tool_translate(const StringName &p_message, const StringName &p_context) const {
+	if (tool_translation.is_valid()) {
+		StringName r = tool_translation->get_message(p_message, p_context);
+		if (r) {
+			return r;
+		}
+	}
+	return p_message;
+}
+
+StringName TranslationServer::tool_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context) const {
+	if (tool_translation.is_valid()) {
+		StringName r = tool_translation->get_plural_message(p_message, p_message_plural, p_n, p_context);
+		if (r) {
+			return r;
+		}
+	}
+
+	if (p_n == 1) {
+		return p_message;
+	}
+	return p_message_plural;
+}
+
+void TranslationServer::set_property_translation(const Ref<Translation> &p_translation) {
+	property_translation = p_translation;
+}
+
+StringName TranslationServer::property_translate(const StringName &p_message, const StringName &p_context) const {
+	if (property_translation.is_valid()) {
+		StringName r = property_translation->get_message(p_message, p_context);
+		if (r) {
+			return r;
+		}
+	}
+	return p_message;
+}
+
+void TranslationServer::set_doc_translation(const Ref<Translation> &p_translation) {
+	doc_translation = p_translation;
+}
+
+StringName TranslationServer::doc_translate(const StringName &p_message, const StringName &p_context) const {
+	if (doc_translation.is_valid()) {
+		StringName r = doc_translation->get_message(p_message, p_context);
+		if (r) {
+			return r;
+		}
+	}
+	return p_message;
+}
+
+StringName TranslationServer::doc_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context) const {
+	if (doc_translation.is_valid()) {
+		StringName r = doc_translation->get_plural_message(p_message, p_message_plural, p_n, p_context);
+		if (r) {
+			return r;
+		}
+	}
+
+	if (p_n == 1) {
+		return p_message;
+	}
+	return p_message_plural;
+}
+
+void TranslationServer::set_extractable_translation(const Ref<Translation> &p_translation) {
+	extractable_translation = p_translation;
+}
+
+StringName TranslationServer::extractable_translate(const StringName &p_message, const StringName &p_context) const {
+	if (extractable_translation.is_valid()) {
+		StringName r = extractable_translation->get_message(p_message, p_context);
+		if (r) {
+			return r;
+		}
+	}
+	return p_message;
+}
+
+StringName TranslationServer::extractable_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context) const {
+	if (extractable_translation.is_valid()) {
+		StringName r = extractable_translation->get_plural_message(p_message, p_message_plural, p_n, p_context);
+		if (r) {
+			return r;
+		}
+	}
+
+	if (p_n == 1) {
+		return p_message;
+	}
+	return p_message_plural;
+}
+
+bool TranslationServer::is_pseudolocalization_enabled() const {
+	return pseudolocalization_enabled;
+}
+
+void TranslationServer::set_pseudolocalization_enabled(bool p_enabled) {
+	pseudolocalization_enabled = p_enabled;
+
+	ResourceLoader::reload_translation_remaps();
+
+	if (OS::get_singleton()->get_main_loop()) {
+		OS::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_TRANSLATION_CHANGED);
+	}
+}
+
+void TranslationServer::reload_pseudolocalization() {
+	pseudolocalization_accents_enabled = GLOBAL_GET("internationalization/pseudolocalization/replace_with_accents");
+	pseudolocalization_double_vowels_enabled = GLOBAL_GET("internationalization/pseudolocalization/double_vowels");
+	pseudolocalization_fake_bidi_enabled = GLOBAL_GET("internationalization/pseudolocalization/fake_bidi");
+	pseudolocalization_override_enabled = GLOBAL_GET("internationalization/pseudolocalization/override");
+	expansion_ratio = GLOBAL_GET("internationalization/pseudolocalization/expansion_ratio");
+	pseudolocalization_prefix = GLOBAL_GET("internationalization/pseudolocalization/prefix");
+	pseudolocalization_suffix = GLOBAL_GET("internationalization/pseudolocalization/suffix");
+	pseudolocalization_skip_placeholders_enabled = GLOBAL_GET("internationalization/pseudolocalization/skip_placeholders");
+
+	ResourceLoader::reload_translation_remaps();
+
+	if (OS::get_singleton()->get_main_loop()) {
+		OS::get_singleton()->get_main_loop()->notification(MainLoop::NOTIFICATION_TRANSLATION_CHANGED);
+	}
+}
+
+StringName TranslationServer::pseudolocalize(const StringName &p_message) const {
+	String message = p_message;
+	int length = message.length();
+	if (pseudolocalization_override_enabled) {
+		message = get_override_string(message);
+	}
+
+	if (pseudolocalization_double_vowels_enabled) {
+		message = double_vowels(message);
+	}
+
+	if (pseudolocalization_accents_enabled) {
+		message = replace_with_accented_string(message);
+	}
+
+	if (pseudolocalization_fake_bidi_enabled) {
+		message = wrap_with_fakebidi_characters(message);
+	}
+
+	StringName res = add_padding(message, length);
+	return res;
+}
+
+StringName TranslationServer::tool_pseudolocalize(const StringName &p_message) const {
+	String message = p_message;
+	message = double_vowels(message);
+	message = replace_with_accented_string(message);
+	StringName res = "[!!! " + message + " !!!]";
+	return res;
+}
+
+String TranslationServer::get_override_string(String &p_message) const {
+	String res;
+	for (int i = 0; i < p_message.length(); i++) {
+		if (pseudolocalization_skip_placeholders_enabled && is_placeholder(p_message, i)) {
+			res += p_message[i];
+			res += p_message[i + 1];
+			i++;
+			continue;
+		}
+		res += '*';
+	}
+	return res;
+}
+
+String TranslationServer::double_vowels(String &p_message) const {
+	String res;
+	for (int i = 0; i < p_message.length(); i++) {
+		if (pseudolocalization_skip_placeholders_enabled && is_placeholder(p_message, i)) {
+			res += p_message[i];
+			res += p_message[i + 1];
+			i++;
+			continue;
+		}
+		res += p_message[i];
+		if (p_message[i] == 'a' || p_message[i] == 'e' || p_message[i] == 'i' || p_message[i] == 'o' || p_message[i] == 'u' ||
+				p_message[i] == 'A' || p_message[i] == 'E' || p_message[i] == 'I' || p_message[i] == 'O' || p_message[i] == 'U') {
+			res += p_message[i];
+		}
+	}
+	return res;
+};
+
+String TranslationServer::replace_with_accented_string(String &p_message) const {
+	String res;
+	for (int i = 0; i < p_message.length(); i++) {
+		if (pseudolocalization_skip_placeholders_enabled && is_placeholder(p_message, i)) {
+			res += p_message[i];
+			res += p_message[i + 1];
+			i++;
+			continue;
+		}
+		const char32_t *accented = get_accented_version(p_message[i]);
+		if (accented) {
+			res += accented;
+		} else {
+			res += p_message[i];
+		}
+	}
+	return res;
+}
+
+String TranslationServer::wrap_with_fakebidi_characters(String &p_message) const {
+	String res;
+	char32_t fakebidiprefix = U'\u202e';
+	char32_t fakebidisuffix = U'\u202c';
+	res += fakebidiprefix;
+	// The fake bidi unicode gets popped at every newline so pushing it back at every newline.
+	for (int i = 0; i < p_message.length(); i++) {
+		if (p_message[i] == '\n') {
+			res += fakebidisuffix;
+			res += p_message[i];
+			res += fakebidiprefix;
+		} else if (pseudolocalization_skip_placeholders_enabled && is_placeholder(p_message, i)) {
+			res += fakebidisuffix;
+			res += p_message[i];
+			res += p_message[i + 1];
+			res += fakebidiprefix;
+			i++;
+		} else {
+			res += p_message[i];
+		}
+	}
+	res += fakebidisuffix;
+	return res;
+}
+
+String TranslationServer::add_padding(const String &p_message, int p_length) const {
+	String underscores = String("_").repeat(p_length * expansion_ratio / 2);
+	String prefix = pseudolocalization_prefix + underscores;
+	String suffix = underscores + pseudolocalization_suffix;
+
+	return prefix + p_message + suffix;
+}
+
+const char32_t *TranslationServer::get_accented_version(char32_t p_character) const {
+	if (!is_ascii_alphabet_char(p_character)) {
+		return nullptr;
+	}
+
+	for (unsigned int i = 0; i < sizeof(_character_to_accented) / sizeof(_character_to_accented[0]); i++) {
+		if (_character_to_accented[i].character == p_character) {
+			return _character_to_accented[i].accented_character;
+		}
+	}
+
+	return nullptr;
+}
+
+bool TranslationServer::is_placeholder(String &p_message, int p_index) const {
+	return p_index < p_message.length() - 1 && p_message[p_index] == '%' &&
+			(p_message[p_index + 1] == 's' || p_message[p_index + 1] == 'c' || p_message[p_index + 1] == 'd' ||
+					p_message[p_index + 1] == 'o' || p_message[p_index + 1] == 'x' || p_message[p_index + 1] == 'X' || p_message[p_index + 1] == 'f');
+}
+
+#ifdef TOOLS_ENABLED
+void TranslationServer::get_argument_options(const StringName &p_function, int p_idx, List<String> *r_options) const {
+	const String pf = p_function;
+	if (p_idx == 0) {
+		HashMap<String, String> *target_hash_map = nullptr;
+		if (pf == "get_language_name") {
+			target_hash_map = &language_map;
+		} else if (pf == "get_script_name") {
+			target_hash_map = &script_map;
+		} else if (pf == "get_country_name") {
+			target_hash_map = &country_name_map;
+		}
+
+		if (target_hash_map) {
+			for (const KeyValue<String, String> &E : *target_hash_map) {
+				r_options->push_back(E.key.quote());
+			}
+		}
+	}
+	Object::get_argument_options(p_function, p_idx, r_options);
+}
+#endif // TOOLS_ENABLED
+
+void TranslationServer::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("set_locale", "locale"), &TranslationServer::set_locale);
+	ClassDB::bind_method(D_METHOD("get_locale"), &TranslationServer::get_locale);
+	ClassDB::bind_method(D_METHOD("get_tool_locale"), &TranslationServer::get_tool_locale);
+
+	ClassDB::bind_method(D_METHOD("compare_locales", "locale_a", "locale_b"), &TranslationServer::compare_locales);
+	ClassDB::bind_method(D_METHOD("standardize_locale", "locale"), &TranslationServer::standardize_locale);
+
+	ClassDB::bind_method(D_METHOD("get_all_languages"), &TranslationServer::get_all_languages);
+	ClassDB::bind_method(D_METHOD("get_language_name", "language"), &TranslationServer::get_language_name);
+
+	ClassDB::bind_method(D_METHOD("get_all_scripts"), &TranslationServer::get_all_scripts);
+	ClassDB::bind_method(D_METHOD("get_script_name", "script"), &TranslationServer::get_script_name);
+
+	ClassDB::bind_method(D_METHOD("get_all_countries"), &TranslationServer::get_all_countries);
+	ClassDB::bind_method(D_METHOD("get_country_name", "country"), &TranslationServer::get_country_name);
+
+	ClassDB::bind_method(D_METHOD("get_locale_name", "locale"), &TranslationServer::get_locale_name);
+
+	ClassDB::bind_method(D_METHOD("translate", "message", "context"), &TranslationServer::translate, DEFVAL(StringName()));
+	ClassDB::bind_method(D_METHOD("translate_plural", "message", "plural_message", "n", "context"), &TranslationServer::translate_plural, DEFVAL(StringName()));
+
+	ClassDB::bind_method(D_METHOD("add_translation", "translation"), &TranslationServer::add_translation);
+	ClassDB::bind_method(D_METHOD("remove_translation", "translation"), &TranslationServer::remove_translation);
+	ClassDB::bind_method(D_METHOD("get_translation_object", "locale"), &TranslationServer::get_translation_object);
+
+	ClassDB::bind_method(D_METHOD("clear"), &TranslationServer::clear);
+
+	ClassDB::bind_method(D_METHOD("get_loaded_locales"), &TranslationServer::get_loaded_locales);
+
+	ClassDB::bind_method(D_METHOD("is_pseudolocalization_enabled"), &TranslationServer::is_pseudolocalization_enabled);
+	ClassDB::bind_method(D_METHOD("set_pseudolocalization_enabled", "enabled"), &TranslationServer::set_pseudolocalization_enabled);
+	ClassDB::bind_method(D_METHOD("reload_pseudolocalization"), &TranslationServer::reload_pseudolocalization);
+	ClassDB::bind_method(D_METHOD("pseudolocalize", "message"), &TranslationServer::pseudolocalize);
+	ADD_PROPERTY(PropertyInfo(Variant::Type::BOOL, "pseudolocalization_enabled"), "set_pseudolocalization_enabled", "is_pseudolocalization_enabled");
+}
+
+void TranslationServer::load_translations() {
+	_load_translations("internationalization/locale/translations"); //all
+	_load_translations("internationalization/locale/translations_" + locale.substr(0, 2));
+
+	if (locale.substr(0, 2) != locale) {
+		_load_translations("internationalization/locale/translations_" + locale);
+	}
+}
+
+TranslationServer::TranslationServer() {
+	singleton = this;
+	init_locale_info();
+}
diff --git a/core/string/translation_server.h b/core/string/translation_server.h
new file mode 100644
index 0000000000..ebe81d9712
--- /dev/null
+++ b/core/string/translation_server.h
@@ -0,0 +1,164 @@
+/**************************************************************************/
+/*  translation_server.h                                                  */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* Permission is hereby granted, free of charge, to any person obtaining  */
+/* a copy of this software and associated documentation files (the        */
+/* "Software"), to deal in the Software without restriction, including    */
+/* without limitation the rights to use, copy, modify, merge, publish,    */
+/* distribute, sublicense, and/or sell copies of the Software, and to     */
+/* permit persons to whom the Software is furnished to do so, subject to  */
+/* the following conditions:                                              */
+/*                                                                        */
+/* The above copyright notice and this permission notice shall be         */
+/* included in all copies or substantial portions of the Software.        */
+/*                                                                        */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF     */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY   */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,   */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
+/**************************************************************************/
+
+#ifndef TRANSLATION_SERVER_H
+#define TRANSLATION_SERVER_H
+
+#include "core/string/translation.h"
+
+class TranslationServer : public Object {
+	GDCLASS(TranslationServer, Object);
+
+	String locale = "en";
+	String fallback;
+
+	HashSet<Ref<Translation>> translations;
+	Ref<Translation> tool_translation;
+	Ref<Translation> property_translation;
+	Ref<Translation> doc_translation;
+	Ref<Translation> extractable_translation;
+
+	bool enabled = true;
+
+	bool pseudolocalization_enabled = false;
+	bool pseudolocalization_accents_enabled = false;
+	bool pseudolocalization_double_vowels_enabled = false;
+	bool pseudolocalization_fake_bidi_enabled = false;
+	bool pseudolocalization_override_enabled = false;
+	bool pseudolocalization_skip_placeholders_enabled = false;
+	float expansion_ratio = 0.0;
+	String pseudolocalization_prefix;
+	String pseudolocalization_suffix;
+
+	StringName tool_pseudolocalize(const StringName &p_message) const;
+	String get_override_string(String &p_message) const;
+	String double_vowels(String &p_message) const;
+	String replace_with_accented_string(String &p_message) const;
+	String wrap_with_fakebidi_characters(String &p_message) const;
+	String add_padding(const String &p_message, int p_length) const;
+	const char32_t *get_accented_version(char32_t p_character) const;
+	bool is_placeholder(String &p_message, int p_index) const;
+
+	static TranslationServer *singleton;
+	bool _load_translations(const String &p_from);
+	String _standardize_locale(const String &p_locale, bool p_add_defaults) const;
+
+	StringName _get_message_from_translations(const StringName &p_message, const StringName &p_context, const String &p_locale, bool plural, const String &p_message_plural = "", int p_n = 0) const;
+
+	static void _bind_methods();
+
+#ifndef DISABLE_DEPRECATED
+	static void _bind_compatibility_methods();
+#endif
+
+	struct LocaleScriptInfo {
+		String name;
+		String script;
+		String default_country;
+		HashSet<String> supported_countries;
+	};
+	static Vector<LocaleScriptInfo> locale_script_info;
+
+	static HashMap<String, String> language_map;
+	static HashMap<String, String> script_map;
+	static HashMap<String, String> locale_rename_map;
+	static HashMap<String, String> country_name_map;
+	static HashMap<String, String> country_rename_map;
+	static HashMap<String, String> variant_map;
+
+	void init_locale_info();
+
+public:
+	_FORCE_INLINE_ static TranslationServer *get_singleton() { return singleton; }
+
+	void set_enabled(bool p_enabled) { enabled = p_enabled; }
+	_FORCE_INLINE_ bool is_enabled() const { return enabled; }
+
+	void set_locale(const String &p_locale);
+	String get_locale() const;
+	Ref<Translation> get_translation_object(const String &p_locale);
+
+	Vector<String> get_all_languages() const;
+	String get_language_name(const String &p_language) const;
+
+	Vector<String> get_all_scripts() const;
+	String get_script_name(const String &p_script) const;
+
+	Vector<String> get_all_countries() const;
+	String get_country_name(const String &p_country) const;
+
+	String get_locale_name(const String &p_locale) const;
+
+	PackedStringArray get_loaded_locales() const;
+
+	void add_translation(const Ref<Translation> &p_translation);
+	void remove_translation(const Ref<Translation> &p_translation);
+
+	StringName translate(const StringName &p_message, const StringName &p_context = "") const;
+	StringName translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context = "") const;
+
+	StringName pseudolocalize(const StringName &p_message) const;
+
+	bool is_pseudolocalization_enabled() const;
+	void set_pseudolocalization_enabled(bool p_enabled);
+	void reload_pseudolocalization();
+
+	String standardize_locale(const String &p_locale) const;
+
+	int compare_locales(const String &p_locale_a, const String &p_locale_b) const;
+
+	String get_tool_locale();
+	void set_tool_translation(const Ref<Translation> &p_translation);
+	Ref<Translation> get_tool_translation() const;
+	StringName tool_translate(const StringName &p_message, const StringName &p_context = "") const;
+	StringName tool_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context = "") const;
+	void set_property_translation(const Ref<Translation> &p_translation);
+	StringName property_translate(const StringName &p_message, const StringName &p_context = "") const;
+	void set_doc_translation(const Ref<Translation> &p_translation);
+	StringName doc_translate(const StringName &p_message, const StringName &p_context = "") const;
+	StringName doc_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context = "") const;
+	void set_extractable_translation(const Ref<Translation> &p_translation);
+	StringName extractable_translate(const StringName &p_message, const StringName &p_context = "") const;
+	StringName extractable_translate_plural(const StringName &p_message, const StringName &p_message_plural, int p_n, const StringName &p_context = "") const;
+
+	void setup();
+
+	void clear();
+
+	void load_translations();
+
+#ifdef TOOLS_ENABLED
+	virtual void get_argument_options(const StringName &p_function, int p_idx, List<String> *r_options) const override;
+#endif // TOOLS_ENABLED
+
+	TranslationServer();
+};
+
+#endif // TRANSLATION_SERVER_H
diff --git a/core/string/ustring.cpp b/core/string/ustring.cpp
index 3d37e17ef8..2683addd4b 100644
--- a/core/string/ustring.cpp
+++ b/core/string/ustring.cpp
@@ -36,7 +36,7 @@
 #include "core/os/memory.h"
 #include "core/string/print_string.h"
 #include "core/string/string_name.h"
-#include "core/string/translation.h"
+#include "core/string/translation_server.h"
 #include "core/string/ucaps.h"
 #include "core/variant/variant.h"
 #include "core/version_generated.gen.h"
@@ -1537,13 +1537,16 @@ Vector<double> String::split_floats(const String &p_splitter, bool p_allow_empty
 	int from = 0;
 	int len = length();
 
+	String buffer = *this;
 	while (true) {
 		int end = find(p_splitter, from);
 		if (end < 0) {
 			end = len;
 		}
 		if (p_allow_empty || (end > from)) {
-			ret.push_back(String::to_float(&get_data()[from]));
+			buffer[end] = 0;
+			ret.push_back(String::to_float(&buffer.get_data()[from]));
+			buffer[end] = _cowdata.get(end);
 		}
 
 		if (end == len) {
@@ -1561,6 +1564,7 @@ Vector<float> String::split_floats_mk(const Vector<String> &p_splitters, bool p_
 	int from = 0;
 	int len = length();
 
+	String buffer = *this;
 	while (true) {
 		int idx;
 		int end = findmk(p_splitters, from, &idx);
@@ -1572,7 +1576,9 @@ Vector<float> String::split_floats_mk(const Vector<String> &p_splitters, bool p_
 		}
 
 		if (p_allow_empty || (end > from)) {
-			ret.push_back(String::to_float(&get_data()[from]));
+			buffer[end] = 0;
+			ret.push_back(String::to_float(&buffer.get_data()[from]));
+			buffer[end] = _cowdata.get(end);
 		}
 
 		if (end == len) {
@@ -1639,13 +1645,43 @@ Vector<int> String::split_ints_mk(const Vector<String> &p_splitters, bool p_allo
 }
 
 String String::join(const Vector<String> &parts) const {
+	if (parts.is_empty()) {
+		return String();
+	} else if (parts.size() == 1) {
+		return parts[0];
+	}
+
+	const int this_length = length();
+
+	int new_size = (parts.size() - 1) * this_length;
+	for (const String &part : parts) {
+		new_size += part.length();
+	}
+	new_size += 1;
+
 	String ret;
-	for (int i = 0; i < parts.size(); ++i) {
-		if (i > 0) {
-			ret += *this;
+	ret.resize(new_size);
+	char32_t *ret_ptrw = ret.ptrw();
+	const char32_t *this_ptr = ptr();
+
+	bool first = true;
+	for (const String &part : parts) {
+		if (first) {
+			first = false;
+		} else if (this_length) {
+			memcpy(ret_ptrw, this_ptr, this_length * sizeof(char32_t));
+			ret_ptrw += this_length;
+		}
+
+		const int part_length = part.length();
+		if (part_length) {
+			memcpy(ret_ptrw, part.ptr(), part_length * sizeof(char32_t));
+			ret_ptrw += part_length;
 		}
-		ret += parts[i];
 	}
+
+	*ret_ptrw = 0;
+
 	return ret;
 }
 
@@ -1658,30 +1694,40 @@ char32_t String::char_lowercase(char32_t p_char) {
 }
 
 String String::to_upper() const {
-	String upper = *this;
+	if (is_empty()) {
+		return *this;
+	}
 
-	for (int i = 0; i < upper.size(); i++) {
-		const char32_t s = upper[i];
-		const char32_t t = _find_upper(s);
-		if (s != t) { // avoid copy on write
-			upper[i] = t;
-		}
+	String upper;
+	upper.resize(size());
+	const char32_t *old_ptr = ptr();
+	char32_t *upper_ptrw = upper.ptrw();
+
+	while (*old_ptr) {
+		*upper_ptrw++ = _find_upper(*old_ptr++);
 	}
 
+	*upper_ptrw = 0;
+
 	return upper;
 }
 
 String String::to_lower() const {
-	String lower = *this;
+	if (is_empty()) {
+		return *this;
+	}
 
-	for (int i = 0; i < lower.size(); i++) {
-		const char32_t s = lower[i];
-		const char32_t t = _find_lower(s);
-		if (s != t) { // avoid copy on write
-			lower[i] = t;
-		}
+	String lower;
+	lower.resize(size());
+	const char32_t *old_ptr = ptr();
+	char32_t *lower_ptrw = lower.ptrw();
+
+	while (*old_ptr) {
+		*lower_ptrw++ = _find_lower(*old_ptr++);
 	}
 
+	*lower_ptrw = 0;
+
 	return lower;
 }
 
@@ -1919,15 +1965,16 @@ String String::hex_encode_buffer(const uint8_t *p_buffer, int p_len) {
 	static const char hex[16] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
 
 	String ret;
-	char v[2] = { 0, 0 };
+	ret.resize(p_len * 2 + 1);
+	char32_t *ret_ptrw = ret.ptrw();
 
 	for (int i = 0; i < p_len; i++) {
-		v[0] = hex[p_buffer[i] >> 4];
-		ret += v;
-		v[0] = hex[p_buffer[i] & 0xF];
-		ret += v;
+		*ret_ptrw++ = hex[p_buffer[i] >> 4];
+		*ret_ptrw++ = hex[p_buffer[i] & 0xF];
 	}
 
+	*ret_ptrw = 0;
+
 	return ret;
 }
 
@@ -1950,11 +1997,12 @@ Vector<uint8_t> String::hex_decode() const {
 	Vector<uint8_t> out;
 	int len = length() / 2;
 	out.resize(len);
+	uint8_t *out_ptrw = out.ptrw();
 	for (int i = 0; i < len; i++) {
 		char32_t c;
 		HEX_TO_BYTE(first, i * 2);
 		HEX_TO_BYTE(second, i * 2 + 1);
-		out.write[i] = first * 16 + second;
+		out_ptrw[i] = first * 16 + second;
 	}
 	return out;
 #undef HEX_TO_BYTE
@@ -1975,14 +2023,16 @@ CharString String::ascii(bool p_allow_extended) const {
 
 	CharString cs;
 	cs.resize(size());
+	char *cs_ptrw = cs.ptrw();
+	const char32_t *this_ptr = ptr();
 
 	for (int i = 0; i < size(); i++) {
-		char32_t c = operator[](i);
+		char32_t c = this_ptr[i];
 		if ((c <= 0x7f) || (c <= 0xff && p_allow_extended)) {
-			cs[i] = c;
+			cs_ptrw[i] = c;
 		} else {
 			print_unicode_error(vformat("Invalid unicode codepoint (%x), cannot represent as ASCII/Latin-1", (uint32_t)c));
-			cs[i] = 0x20; // ascii doesn't have a replacement character like unicode, 0x1a is sometimes used but is kinda arcane
+			cs_ptrw[i] = 0x20; // ASCII doesn't have a replacement character like unicode, 0x1a is sometimes used but is kinda arcane.
 		}
 	}
 
@@ -3115,8 +3165,9 @@ Vector<uint8_t> String::md5_buffer() const {
 
 	Vector<uint8_t> ret;
 	ret.resize(16);
+	uint8_t *ret_ptrw = ret.ptrw();
 	for (int i = 0; i < 16; i++) {
-		ret.write[i] = hash[i];
+		ret_ptrw[i] = hash[i];
 	}
 	return ret;
 }
@@ -3128,8 +3179,9 @@ Vector<uint8_t> String::sha1_buffer() const {
 
 	Vector<uint8_t> ret;
 	ret.resize(20);
+	uint8_t *ret_ptrw = ret.ptrw();
 	for (int i = 0; i < 20; i++) {
-		ret.write[i] = hash[i];
+		ret_ptrw[i] = hash[i];
 	}
 
 	return ret;
@@ -3142,14 +3194,15 @@ Vector<uint8_t> String::sha256_buffer() const {
 
 	Vector<uint8_t> ret;
 	ret.resize(32);
+	uint8_t *ret_ptrw = ret.ptrw();
 	for (int i = 0; i < 32; i++) {
-		ret.write[i] = hash[i];
+		ret_ptrw[i] = hash[i];
 	}
 	return ret;
 }
 
 String String::insert(int p_at_pos, const String &p_string) const {
-	if (p_at_pos < 0) {
+	if (p_string.is_empty() || p_at_pos < 0) {
 		return *this;
 	}
 
@@ -3157,17 +3210,27 @@ String String::insert(int p_at_pos, const String &p_string) const {
 		p_at_pos = length();
 	}
 
-	String pre;
+	String ret;
+	ret.resize(length() + p_string.length() + 1);
+	char32_t *ret_ptrw = ret.ptrw();
+	const char32_t *this_ptr = ptr();
+
 	if (p_at_pos > 0) {
-		pre = substr(0, p_at_pos);
+		memcpy(ret_ptrw, this_ptr, p_at_pos * sizeof(char32_t));
+		ret_ptrw += p_at_pos;
 	}
 
-	String post;
+	memcpy(ret_ptrw, p_string.ptr(), p_string.length() * sizeof(char32_t));
+	ret_ptrw += p_string.length();
+
 	if (p_at_pos < length()) {
-		post = substr(p_at_pos, length() - p_at_pos);
+		memcpy(ret_ptrw, this_ptr + p_at_pos, (length() - p_at_pos) * sizeof(char32_t));
+		ret_ptrw += length() - p_at_pos;
 	}
 
-	return pre + p_string + post;
+	*ret_ptrw = 0;
+
+	return ret;
 }
 
 String String::erase(int p_pos, int p_chars) const {
@@ -3871,8 +3934,9 @@ Vector<String> String::bigrams() const {
 		return b;
 	}
 	b.resize(n_pairs);
+	String *b_ptrw = b.ptrw();
 	for (int i = 0; i < n_pairs; i++) {
-		b.write[i] = substr(i, 2);
+		b_ptrw[i] = substr(i, 2);
 	}
 	return b;
 }
@@ -3986,54 +4050,161 @@ String String::format(const Variant &values, const String &placeholder) const {
 	return new_string;
 }
 
-String String::replace(const String &p_key, const String &p_with) const {
-	String new_string;
+static String _replace_common(const String &p_this, const String &p_key, const String &p_with, bool p_case_insensitive) {
+	if (p_key.is_empty() || p_this.is_empty()) {
+		return p_this;
+	}
+
+	const int key_length = p_key.length();
+
 	int search_from = 0;
 	int result = 0;
 
-	while ((result = find(p_key, search_from)) >= 0) {
-		new_string += substr(search_from, result - search_from);
-		new_string += p_with;
-		search_from = result + p_key.length();
+	LocalVector<int> found;
+
+	while ((result = (p_case_insensitive ? p_this.findn(p_key, search_from) : p_this.find(p_key, search_from))) >= 0) {
+		found.push_back(result);
+		search_from = result + key_length;
 	}
 
-	if (search_from == 0) {
-		return *this;
+	if (found.is_empty()) {
+		return p_this;
+	}
+
+	String new_string;
+
+	const int with_length = p_with.length();
+	const int old_length = p_this.length();
+
+	new_string.resize(old_length + found.size() * (with_length - key_length) + 1);
+
+	char32_t *new_ptrw = new_string.ptrw();
+	const char32_t *old_ptr = p_this.ptr();
+	const char32_t *with_ptr = p_with.ptr();
+
+	int last_pos = 0;
+
+	for (const int &pos : found) {
+		if (last_pos != pos) {
+			memcpy(new_ptrw, old_ptr + last_pos, (pos - last_pos) * sizeof(char32_t));
+			new_ptrw += (pos - last_pos);
+		}
+		if (with_length) {
+			memcpy(new_ptrw, with_ptr, with_length * sizeof(char32_t));
+			new_ptrw += with_length;
+		}
+		last_pos = pos + key_length;
+	}
+
+	if (last_pos != old_length) {
+		memcpy(new_ptrw, old_ptr + last_pos, (old_length - last_pos) * sizeof(char32_t));
+		new_ptrw += old_length - last_pos;
 	}
 
-	new_string += substr(search_from, length() - search_from);
+	*new_ptrw = 0;
 
 	return new_string;
 }
 
-String String::replace(const char *p_key, const char *p_with) const {
-	String new_string;
+static String _replace_common(const String &p_this, char const *p_key, char const *p_with, bool p_case_insensitive) {
+	int key_length = strlen(p_key);
+
+	if (key_length == 0 || p_this.is_empty()) {
+		return p_this;
+	}
+
 	int search_from = 0;
 	int result = 0;
 
-	while ((result = find(p_key, search_from)) >= 0) {
-		new_string += substr(search_from, result - search_from);
-		new_string += p_with;
-		int k = 0;
-		while (p_key[k] != '\0') {
-			k++;
+	LocalVector<int> found;
+
+	while ((result = (p_case_insensitive ? p_this.findn(p_key, search_from) : p_this.find(p_key, search_from))) >= 0) {
+		found.push_back(result);
+		search_from = result + key_length;
+	}
+
+	if (found.is_empty()) {
+		return p_this;
+	}
+
+	String new_string;
+
+	// Create string to speed up copying as we can't do `memcopy` between `char32_t` and `char`.
+	const String with_string(p_with);
+	const int with_length = with_string.length();
+	const int old_length = p_this.length();
+
+	new_string.resize(old_length + found.size() * (with_length - key_length) + 1);
+
+	char32_t *new_ptrw = new_string.ptrw();
+	const char32_t *old_ptr = p_this.ptr();
+	const char32_t *with_ptr = with_string.ptr();
+
+	int last_pos = 0;
+
+	for (const int &pos : found) {
+		if (last_pos != pos) {
+			memcpy(new_ptrw, old_ptr + last_pos, (pos - last_pos) * sizeof(char32_t));
+			new_ptrw += (pos - last_pos);
 		}
-		search_from = result + k;
+		if (with_length) {
+			memcpy(new_ptrw, with_ptr, with_length * sizeof(char32_t));
+			new_ptrw += with_length;
+		}
+		last_pos = pos + key_length;
 	}
 
-	if (search_from == 0) {
-		return *this;
+	if (last_pos != old_length) {
+		memcpy(new_ptrw, old_ptr + last_pos, (old_length - last_pos) * sizeof(char32_t));
+		new_ptrw += old_length - last_pos;
 	}
 
-	new_string += substr(search_from, length() - search_from);
+	*new_ptrw = 0;
 
 	return new_string;
 }
 
+String String::replace(const String &p_key, const String &p_with) const {
+	return _replace_common(*this, p_key, p_with, false);
+}
+
+String String::replace(const char *p_key, const char *p_with) const {
+	return _replace_common(*this, p_key, p_with, false);
+}
+
 String String::replace_first(const String &p_key, const String &p_with) const {
 	int pos = find(p_key);
 	if (pos >= 0) {
-		return substr(0, pos) + p_with + substr(pos + p_key.length(), length());
+		const int old_length = length();
+		const int key_length = p_key.length();
+		const int with_length = p_with.length();
+
+		String new_string;
+		new_string.resize(old_length + (with_length - key_length) + 1);
+
+		char32_t *new_ptrw = new_string.ptrw();
+		const char32_t *old_ptr = ptr();
+		const char32_t *with_ptr = p_with.ptr();
+
+		if (pos > 0) {
+			memcpy(new_ptrw, old_ptr, pos * sizeof(char32_t));
+			new_ptrw += pos;
+		}
+
+		if (with_length) {
+			memcpy(new_ptrw, with_ptr, with_length * sizeof(char32_t));
+			new_ptrw += with_length;
+		}
+		pos += key_length;
+
+		if (pos != old_length) {
+			memcpy(new_ptrw, old_ptr + pos, (old_length - pos) * sizeof(char32_t));
+			new_ptrw += (old_length - pos);
+		}
+
+		*new_ptrw = 0;
+
+		return new_string;
 	}
 
 	return *this;
@@ -4042,55 +4213,45 @@ String String::replace_first(const String &p_key, const String &p_with) const {
 String String::replace_first(const char *p_key, const char *p_with) const {
 	int pos = find(p_key);
 	if (pos >= 0) {
-		int substring_length = strlen(p_key);
-		return substr(0, pos) + p_with + substr(pos + substring_length, length());
-	}
-
-	return *this;
-}
+		const int old_length = length();
+		const int key_length = strlen(p_key);
+		const int with_length = strlen(p_with);
 
-String String::replacen(const String &p_key, const String &p_with) const {
-	String new_string;
-	int search_from = 0;
-	int result = 0;
+		String new_string;
+		new_string.resize(old_length + (with_length - key_length) + 1);
 
-	while ((result = findn(p_key, search_from)) >= 0) {
-		new_string += substr(search_from, result - search_from);
-		new_string += p_with;
-		search_from = result + p_key.length();
-	}
+		char32_t *new_ptrw = new_string.ptrw();
+		const char32_t *old_ptr = ptr();
 
-	if (search_from == 0) {
-		return *this;
-	}
+		if (pos > 0) {
+			memcpy(new_ptrw, old_ptr, pos * sizeof(char32_t));
+			new_ptrw += pos;
+		}
 
-	new_string += substr(search_from, length() - search_from);
-	return new_string;
-}
+		for (int i = 0; i < with_length; ++i) {
+			*new_ptrw++ = p_with[i];
+		}
+		pos += key_length;
 
-String String::replacen(const char *p_key, const char *p_with) const {
-	String new_string;
-	int search_from = 0;
-	int result = 0;
-	int substring_length = strlen(p_key);
+		if (pos != old_length) {
+			memcpy(new_ptrw, old_ptr + pos, (old_length - pos) * sizeof(char32_t));
+			new_ptrw += (old_length - pos);
+		}
 
-	if (substring_length == 0) {
-		return *this; // there's nothing to match or substitute
-	}
+		*new_ptrw = 0;
 
-	while ((result = findn(p_key, search_from)) >= 0) {
-		new_string += substr(search_from, result - search_from);
-		new_string += p_with;
-		search_from = result + substring_length;
+		return new_string;
 	}
 
-	if (search_from == 0) {
-		return *this;
-	}
+	return *this;
+}
 
-	new_string += substr(search_from, length() - search_from);
+String String::replacen(const String &p_key, const String &p_with) const {
+	return _replace_common(*this, p_key, p_with, true);
+}
 
-	return new_string;
+String String::replacen(const char *p_key, const char *p_with) const {
+	return _replace_common(*this, p_key, p_with, true);
 }
 
 String String::repeat(int p_count) const {
@@ -4384,10 +4545,7 @@ String String::simplify_path() const {
 			dirs.remove_at(i);
 			i--;
 		} else if (d == "..") {
-			if (i == 0) {
-				dirs.remove_at(i);
-				i--;
-			} else {
+			if (i != 0) {
 				dirs.remove_at(i);
 				dirs.remove_at(i - 1);
 				i -= 2;
@@ -4466,7 +4624,7 @@ bool String::is_absolute_path() const {
 	}
 }
 
-String String::validate_identifier() const {
+String String::validate_ascii_identifier() const {
 	if (is_empty()) {
 		return "_"; // Empty string is not a valid identifier;
 	}
@@ -4489,7 +4647,7 @@ String String::validate_identifier() const {
 	return result;
 }
 
-bool String::is_valid_identifier() const {
+bool String::is_valid_ascii_identifier() const {
 	int len = length();
 
 	if (len == 0) {
@@ -4511,6 +4669,26 @@ bool String::is_valid_identifier() const {
 	return true;
 }
 
+bool String::is_valid_unicode_identifier() const {
+	const char32_t *str = ptr();
+	int len = length();
+
+	if (len == 0) {
+		return false; // Empty string.
+	}
+
+	if (!is_unicode_identifier_start(str[0])) {
+		return false;
+	}
+
+	for (int i = 1; i < len; i++) {
+		if (!is_unicode_identifier_continue(str[i])) {
+			return false;
+		}
+	}
+	return true;
+}
+
 bool String::is_valid_string() const {
 	int l = length();
 	const char32_t *src = get_data();
@@ -4757,8 +4935,9 @@ String String::xml_unescape() const {
 		return String();
 	}
 	str.resize(len + 1);
-	_xml_unescape(get_data(), l, str.ptrw());
-	str[len] = 0;
+	char32_t *str_ptrw = str.ptrw();
+	_xml_unescape(get_data(), l, str_ptrw);
+	str_ptrw[len] = 0;
 	return str;
 }
 
@@ -5321,6 +5500,11 @@ String String::lpad(int min_length, const String &character) const {
 //   "fish %s %d pie" % ["frog", 12]
 // In case of an error, the string returned is the error description and "error" is true.
 String String::sprintf(const Array &values, bool *error) const {
+	static const String ZERO("0");
+	static const String SPACE(" ");
+	static const String MINUS("-");
+	static const String PLUS("+");
+
 	String formatted;
 	char32_t *self = (char32_t *)get_data();
 	bool in_format = false;
@@ -5343,7 +5527,7 @@ String String::sprintf(const Array &values, bool *error) const {
 		if (in_format) { // We have % - let's see what else we get.
 			switch (c) {
 				case '%': { // Replace %% with %
-					formatted += chr(c);
+					formatted += c;
 					in_format = false;
 					break;
 				}
@@ -5393,7 +5577,7 @@ String String::sprintf(const Array &values, bool *error) const {
 
 					// Padding.
 					int pad_chars_count = (negative || show_sign) ? min_chars - 1 : min_chars;
-					String pad_char = pad_with_zeros ? String("0") : String(" ");
+					const String &pad_char = pad_with_zeros ? ZERO : SPACE;
 					if (left_justified) {
 						str = str.rpad(pad_chars_count, pad_char);
 					} else {
@@ -5402,7 +5586,7 @@ String String::sprintf(const Array &values, bool *error) const {
 
 					// Sign.
 					if (show_sign || negative) {
-						String sign_char = negative ? "-" : "+";
+						const String &sign_char = negative ? MINUS : PLUS;
 						if (left_justified) {
 							str = str.insert(0, sign_char);
 						} else {
@@ -5439,7 +5623,7 @@ String String::sprintf(const Array &values, bool *error) const {
 
 					// Padding. Leave room for sign later if required.
 					int pad_chars_count = (is_negative || show_sign) ? min_chars - 1 : min_chars;
-					String pad_char = (pad_with_zeros && is_finite) ? String("0") : String(" "); // Never pad NaN or inf with zeros
+					const String &pad_char = (pad_with_zeros && is_finite) ? ZERO : SPACE; // Never pad NaN or inf with zeros
 					if (left_justified) {
 						str = str.rpad(pad_chars_count, pad_char);
 					} else {
@@ -5448,7 +5632,7 @@ String String::sprintf(const Array &values, bool *error) const {
 
 					// Add sign if needed.
 					if (show_sign || is_negative) {
-						String sign_char = is_negative ? "-" : "+";
+						const String &sign_char = is_negative ? MINUS : PLUS;
 						if (left_justified) {
 							str = str.insert(0, sign_char);
 						} else {
@@ -5501,7 +5685,7 @@ String String::sprintf(const Array &values, bool *error) const {
 
 						// Padding. Leave room for sign later if required.
 						int pad_chars_count = val < 0 ? min_chars - 1 : min_chars;
-						String pad_char = (pad_with_zeros && is_finite) ? String("0") : String(" "); // Never pad NaN or inf with zeros
+						const String &pad_char = (pad_with_zeros && is_finite) ? ZERO : SPACE; // Never pad NaN or inf with zeros
 						if (left_justified) {
 							number_str = number_str.rpad(pad_chars_count, pad_char);
 						} else {
@@ -5511,9 +5695,9 @@ String String::sprintf(const Array &values, bool *error) const {
 						// Add sign if needed.
 						if (val < 0) {
 							if (left_justified) {
-								number_str = number_str.insert(0, "-");
+								number_str = number_str.insert(0, MINUS);
 							} else {
-								number_str = number_str.insert(pad_with_zeros ? 0 : number_str.length() - initial_len, "-");
+								number_str = number_str.insert(pad_with_zeros ? 0 : number_str.length() - initial_len, MINUS);
 							}
 						}
 
@@ -5678,7 +5862,7 @@ String String::sprintf(const Array &values, bool *error) const {
 					in_decimals = false;
 					break;
 				default:
-					formatted += chr(c);
+					formatted += c;
 			}
 		}
 	}
diff --git a/core/string/ustring.h b/core/string/ustring.h
index 9df2d56e80..11f15031f9 100644
--- a/core/string/ustring.h
+++ b/core/string/ustring.h
@@ -459,10 +459,11 @@ public:
 	// node functions
 	static String get_invalid_node_name_characters(bool p_allow_internal = false);
 	String validate_node_name() const;
-	String validate_identifier() const;
+	String validate_ascii_identifier() const;
 	String validate_filename() const;
 
-	bool is_valid_identifier() const;
+	bool is_valid_ascii_identifier() const;
+	bool is_valid_unicode_identifier() const;
 	bool is_valid_int() const;
 	bool is_valid_float() const;
 	bool is_valid_hex_number(bool p_with_prefix) const;
@@ -470,6 +471,9 @@ public:
 	bool is_valid_ip_address() const;
 	bool is_valid_filename() const;
 
+	// Use `is_valid_ascii_identifier()` instead. Kept for compatibility.
+	bool is_valid_identifier() const { return is_valid_ascii_identifier(); }
+
 	/**
 	 * The constructors must not depend on other overloads
 	 */