Request::getPreferredLanguage PHP Method

        public static function getPreferredLanguage($locales = null)
        {
            //Method inherited from \Symfony\Component\HttpFoundation\Request
            return \Illuminate\Http\Request::getPreferredLanguage($locales);
        }

 /**
  * Sets the locale if it exists in the session or uses preferred or default locale
  *
  * @return void
  */
 public function configureLocale()
 {
     $defaultLocale = static::getDefaultLocale();
     // set fallback locale
     \App('translator')->setFallback($defaultLocale);
     // set main locale
     \Request::setDefaultLocale($defaultLocale);
     $sessionKey = static::getLocaleSessionKey();
     $preferredLocale = \Request::getPreferredLanguage(static::getAllowedLocales());
     \App::setLocale($sessionKey ? \Session::get($sessionKey, $preferredLocale) : $preferredLocale);
 }