public Optional<List<Locale.LanguageRange>> getAcceptableLanguages(final LocalAddress localAddress) {
    return Optional.ofNullable(remoteChannelsByLocalAddress.get(localAddress))
        .map(remoteChannel -> remoteChannel.attr(ACCEPT_LANGUAGE_ATTRIBUTE_KEY).get());
  }
@Test
  void getAcceptableLanguages() {
    clientConnectionManager.handleConnectionEstablished(localChannel, remoteChannel, Optional.empty());

    assertEquals(Optional.empty(),
        clientConnectionManager.getAcceptableLanguages(localChannel.localAddress()));

    final List<Locale.LanguageRange> acceptLanguageRanges = Locale.LanguageRange.parse("en,ja");
    remoteChannel.attr(ClientConnectionManager.ACCEPT_LANGUAGE_ATTRIBUTE_KEY).set(acceptLanguageRanges);

    assertEquals(Optional.of(acceptLanguageRanges),
        clientConnectionManager.getAcceptableLanguages(localChannel.localAddress()));
  }