Not 'for android' but this TTS model is popular https://github.com/coqui-ai/TTS
This one is a little older but works as well: https://github.com/snakers4/silero-models
Both of those are AI models only. Most offline AI is runs over the network already, so like I have it on my phone at home, but it requires setup and I'm connecting to my computer to offload the task on my GPU. Personally my phone doesn't have anywhere near enough RAM to run all of Android's (zygote) bloat even on GrapheneOS and any models I would want to run.
I don't think we are at the point where mobile devices have the hardware specs needed for this to happen natively yet. Maybe it will happen soon though.
That's just what I know, but it is like water cooler talk and not primary source authority by any stretch.