I think this would be great, but as an additional in-app download to pull down the model
This is basically what you’re asking for. The tradeoff is that we add a dependency to Google, and requires storing translation models offline on disk and memory which can take a good amount of space. This is also what Amethyst does on Android. I’m happy to explore this translation approach as an option for Damus.
https://developers.google.com/ml-kit/language/translation/ios
Discussion
I use Amethyst. It automatically translates from all languages. But it is not perfect.