TTSUtteranceListener.kt

textToSpeech.setOnUtteranceProgressListener(object : UtteranceProgressListener() {

    override fun onDone(utteranceId: String?) {
      //do whatever you want when TTS finish speaking.
    }

    override fun onError(utteranceId: String?) {
      //do whatever you want if TTS makes an error.
    }

    override fun onStart(utteranceId: String?) {
      //do whatever you want when TTS start speaking.
    }
})