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;
    }