private function isCacheExpired()
    {
        if (empty($this->cacheInterval)) {
            return true;
        }

        $cache_file = $this->cacheDirectory.'/translations/cache_timestamp';
        $cache_dir  =$this->cacheDirectory.'/translations';
        if ('\\' === DIRECTORY_SEPARATOR) {
            $cache_file = strtr($cache_file, '/', '\\');
            $cache_dir = strtr($cache_dir, '/', '\\');
        }
        if (!\is_dir($cache_dir)) {
            \mkdir($cache_dir);
        }        
        if (!\file_exists($cache_file)) {
            \touch($cache_file);
            return true;
        }
        $expired = false;
        if ((\time() - \filemtime($cache_file)) > $this->cacheInterval) {
            \file_put_contents($cache_file, \time());
            $expired = true;
        }

        return $expired;
    }