code: public String _(String key, Object... args) {
  //        JellyBuilder b = (JellyBuilder)getDelegate();
  
          ResourceBundle resourceBundle = getResourceBundle();
  
          // notify the listener if set
  //        InternationalizedStringExpressionListener listener = (InternationalizedStringExpressionListener) Stapler.getCurrentRequest().getAttribute(LISTENER_NAME);
  //        if(listener!=null)
  //            listener.onUsed(this, args);
  
          args = Stapler.htmlSafeArguments(args);
  
          return resourceBundle.format(LocaleProvider.getLocale(), key, args);
      }
docs: Looks up the resource bundle with the given key, formats with arguments,
  then return that formatted string.