Sending a User Message.

UserMessage.java

//User Message
List<String> translationTargetLanguages = new ArrayList<>();
translationTargetLanguages.add("fr");       // French
translationTargetLanguages.add("de");       // German

UserMessageParams params = new UserMessageParams()
        .setMessage(TEXT_MESSAGE)
        .setCustomType(CUSTOM_TYPE)
        .setData(DATA)
        .setTranslationTargetLanguages(translationTargetLanguages)

groupChannel.sendUserMessage(params, new BaseChannel.SendUserMessageHandler() {
    @Override
    public void onSent(UserMessage userMessage, SendBirdException e) {
        if (e != null) {    // Error.
            return;
        }
    }
});