code: private static boolean isISO639LanguageCode(final String str) {
          return StringUtils.isAllLowerCase(str) && (str.length() == 2 || str.length() == 3);
      }
docs: Checks whether the given String is a ISO 639 compliant language code.
  
  @param str the String to check.
  @return true, if the given String is a ISO 639 compliant language code.