I was in your shoes for ages, but HeliBoard has predictions and other languages out of the box. Voice transcription works if you have FUTO Voice Input. Gesture typing uses a swypelibs binary extracted from Gapps; you just have to download it manually since the app never requests network access (instructions are on the Github page). I started using it today and some of its features actually seem to work better for me than Gboard, like the swipe gestures on delete or space, and it has at least a few more features I’m pretty sure Gboard doesn’t. Give it a look at least.