public static function setAppFallbackLocale()
    {
        if (Session::has('fallback_locale')) {
            Lang::setFallback(Session::get('fallback_locale'));
        }
        elseif (
            ($user = BackendAuth::getUser()) &&
            ($locale = static::get('fallback_locale'))
        ) {
            Session::put('fallback_locale', $locale);
            Lang::setFallback($locale);
        }
    }