setLanguage method
Sets the language
to the given value. While the language should be one
in the supportedLanguages list, that is not actually a requirement.
Setting the language
to one that is not part of the supportedLanguages
will result in the cached values being cleared and default strings being
used until / unless the application applies the new translation values via
the apply function.
Implementation
Future<void> setLanguage(String language) {
_language = language;
_translations.clear();
_translationsStreamController?.add(null);
return _load(_loaders[language]);
}