code: public String getFormatString(Locale locale, String key) {
          String[] suffixes = toStrings(locale);
  
          while(true) {
              for (int i=0; i<suffixes.length; i++) {
                  String suffix = suffixes[i];
                  String msg = get(suffix).getProperty(key);
                  if(msg!=null && msg.length()>0)
                      // ignore a definition without value, because stapler:i18n generates
                      // value-less definitions
                      return msg;
  
                  int idx = suffix.lastIndexOf('_');
                  if(idx<0)   // failed to find
                      return null;
                  suffixes[i] = suffix.substring(0,idx);
              }
          }
      }
docs: Gets the format string for the given key.
  <p>
  This method performs a search so that a look up for "pt_BR" would delegate
  to "pt" then "" (the no-locale locale.)