public static function enablePageCache($language = 'en', $currency = 'usd')
 {
     if (!session_id()) {
         session_start();
     }
     if (self::canPageCache()) {
         self::$page_cache_file = Journal2Cache::$path . '/' . Journal2Cache::$dir . implode('_', array(md5(self::getCurrentUrl()), $language, $currency, self::$device));
         if (file_exists(self::$page_cache_file)) {
             echo file_get_contents(self::$page_cache_file);
             exit;
         }
     }
 }