Replace en_US code with en when searching for user preferred languages (#3859)

Source/options.cpp

@@ -1030,7 +1030,12 @@ void OptionEntryLanguageCode::LoadFromIni(string_view category)
 	locales.emplace_back(std::locale("").name().substr(0, 5));
 #endif
 
-	// Insert non-regional locale codes after the last regional variation so we fallback to neutral translations if no regional translation exists that meets user preferences.
+	// So that the correct language is shown in the settings menu for users with US english set as a preferred language
+	//  we need to replace the "en_US" locale code with the neutral string "en" as expected by the available options
+	std::replace(locales.begin(), locales.end(), std::string { "en_US" }, std::string { "en" });
+
+	// Insert non-regional locale codes after the last regional variation so we fallback to neutral translations if no
+	//  regional translation exists that meets user preferences.
 	for (auto localeIter = locales.rbegin(); localeIter != locales.rend(); localeIter++) {
 		auto regionSeparator = localeIter->find('_');
 		if (regionSeparator != std::string::npos) {

Source/utils/language.cpp

@@ -270,8 +270,9 @@ const std::string &LanguageTranslate(const char *key)
 
 bool HasTranslation(const std::string &locale)
 {
-	if (locale == "en" || locale == "en_US") {
-		// the base translation is en_US. No translation file will be present for these codes but we want the check to succeed to prevent further searches.
+	if (locale == "en") {
+		// the base translation is en (really en_US). No translation file will be present for this code but we want
+		//  the check to succeed to prevent further searches.
 		return true;
 	}