code: public ULocale[] getRuleSetDisplayNameLocales() {
          if (ruleSetDisplayNames != null) {
              Set<String> s = ruleSetDisplayNames.keySet();
              String[] locales = s.toArray(new String[s.size()]);
              Arrays.sort(locales, String.CASE_INSENSITIVE_ORDER);
              ULocale[] result = new ULocale[locales.length];
              for (int i = 0; i < locales.length; ++i) {
                  result[i] = new ULocale(locales[i]);
              }
              return result;
          }
          return null;
      }
docs: Return a list of locales for which there are locale-specific display names
  for the rule sets in this formatter.  If there are no localized display names, return null.
  @return an array of the ULocales for which there is rule set display name information