code: public String format(String key, Object ... params) {
          ResourceBundle bundle = getBundle();
          if (bundle.containsKey(key)) {
              String msg = bundle.getString(key);
              return MessageFormat.format(msg, params);
          } else {
              return MessageFormat.format("!!{0}!!", key); //$NON-NLS-1$
          }
      }
docs: Look up a message in the i18n resource message bundle by key, then format the
  message with the given params and return the result.
  @param key the key
  @param params the parameters
  @return formatted string