code: public function getAcceptableLanguages()
      {
          if ($this->_languages === null) {
              if ($this->headers->has('Accept-Language')) {
                  $this->_languages = array_keys($this->parseAcceptHeader($this->headers->get('Accept-Language')));
              } else {
                  $this->_languages = [];
              }
          }
  
          return $this->_languages;
      }
docs: Returns the languages acceptable by the end user.
  This is determined by the `Accept-Language` HTTP header.
  @return array the languages ordered by the preference level. The first element
  represents the most preferred language.