docs: public static List<Locale> countriesByLanguage(String languageCode)
      {
          if (languageCode == null)
          {
              return Collections.emptyList();
          }
          List<Locale> countries = COUNTRIES_BY_LANGUAGE.get(languageCode);
          if (countries == null)
          {
              countries = new ArrayList<Locale>();
              List<Locale> locales = availableLocaleList();
              for (int i = 0; i < locales.size(); i++)
              {
                  Locale locale = locales.get(i);
                  if (languageCode.equals(locale.getLanguage()) &&
                          locale.getCountry().length() != 0 &&
                          locale.getVariant().length() == 0)
                  {
                      countries.add(locale);
                  }
              }
              countries = Collections.unmodifiableList(countries);
              COUNTRIES_BY_LANGUAGE.putIfAbsent(languageCode, countries);
              countries = COUNTRIES_BY_LANGUAGE.get(languageCode);
          }
          return countries;
      }