Basic struct
I18n::getConfig(): Get config
Exceptions: classes of basic exceptions
I18n::getCurrentLanguage(): Get current language
I18n::setCurrentLanguage(): Set current language
I18n::getDefaultLanguage(): Get default language
I18n::getParentLanguage(): Get parent language
I18n::isDefault(): Is current of default?
I18n::isLanguageExists(): Check whether there is a language