code: protected String key(String keyName, Locale locale) {
  
          CmsMessages messages = getMessages(locale);
          if (messages != null) {
              return messages.key(keyName);
          }
          return CmsMessages.formatUnknownKey(keyName);
      }
docs: Returns the localized resource string for a given message key according to the configured resource bundle
  of this content handler.<p>
  
  If the key was not found in the configured bundle, or no bundle is configured for this
  content handler, the return value is
  <code>"??? " + keyName + " ???"</code>.<p>
  
  @param keyName the key for the desired string
  @param locale the locale to get the key from
  
  @return the resource string for the given key
  
  @see CmsMessages#formatUnknownKey(String)
  @see CmsMessages#isUnknownKey(String)