code: public static final String[] getKeywordValuesForLocale(String key, ULocale locale,
                                                             boolean commonlyUsed) {
          // Note: The parameter commonlyUsed is not used.
          // The switch is in the method signature for consistency
          // with other locale services.
  
          // Read available collation values from collation bundles.
          ICUResourceBundle bundle = (ICUResourceBundle)
                  UResourceBundle.getBundleInstance(
                          ICUData.ICU_COLLATION_BASE_NAME, locale);
          KeywordsSink sink = new KeywordsSink();
          bundle.getAllItemsWithFallback("collations", sink);
          return sink.values.toArray(new String[sink.values.size()]);
      }
docs: <strong>[icu]</strong> Given a key and a locale, returns an array of string values in a preferred
  order that would make a difference. These are all and only those values where
  the open (creation) of the service with the locale formed from the input locale
  plus input keyword and that value has different behavior than creation with the
  input locale alone.
  @param key           one of the keys supported by this service.  For now, only
  "collation" is supported.
  @param locale        the locale
  @param commonlyUsed  if set to true it will return only commonly used values
  with the given locale in preferred order.  Otherwise,
  it will return all the available values for the locale.
  @return an array of string values for the given key and the locale.