code: public Translation addTranslation(String locale, String value) {
          return addTranslation(locale, value, false);
      }
docs: Saves or updates the translation for the specified locale.
  If the key was outdated, checks if the key is still outdated.
  
  @param locale specified the translation locale
  @param value  translation value
  @return the new translation
  @throws java.lang.IllegalArgumentException if the locale is null or empty
  or contains other characters than letters and "-".