I can't speak to home assistant specifically, but the last time I looked at voice models, supporting multiple languages and doing it Really Well just happens to require a model with a massive amount of RAM, especially to run at anything resembling real-time.

It's be awesome if they open sourced that model though, or published what models they're using. But I think it unlikely to happen because home assistant is a sorta funnel to nabu casa

That said, from what I can find, it sounds like Assist can be run without the hardware, either with or without the cloud upgrade. So you could definitely use your own hardware, headset, speakers, etc. to play with Assist