Piwik\Plugins\LanguagesManager\LanguagesManager::setLanguageForSession PHP Method

    public static function setLanguageForSession($languageCode)
    {
        if (!API::getInstance()->isLanguageAvailable($languageCode)) {
            return false;
        }
        $cookieName = Config::getInstance()->General['language_cookie_name'];
        $cookie = new Cookie($cookieName, 0);
        $cookie->set('language', $languageCode);
        $cookie->save();
        return true;
    }

 /**
  * anonymous = in the session
  * authenticated user = in the session
  */
 public function saveLanguage()
 {
     $language = Common::getRequestVar('language');
     // Prevent CSRF only when piwik is not installed yet (During install user can change language)
     if (DbHelper::isInstalled()) {
         $this->checkTokenInUrl();
     }
     LanguagesManager::setLanguageForSession($language);
     Url::redirectToReferrer();
 }