Piwik\Tracker\Request::getBrowserLanguage PHP Method

    public function getBrowserLanguage()
    {
        return Common::getRequestVar('lang', Common::getBrowserLanguage(), 'string', $this->params);
    }

 /**
  * @param Request $request
  * @param Visitor $visitor
  * @param Action|null $action
  * @return mixed
  */
 public function onNewVisit(Request $request, Visitor $visitor, $action)
 {
     $language = $request->getBrowserLanguage();
     if (empty($language)) {
         return '';
     }
     return substr($language, 0, 20);
 }