This was what kept me on Microsoft's keyboard for ages, I've been using using this fork for the past month or two and it's by far the best FOSS keyboard for multilingual typing and autocorrect. Maybe not quite as polished as GBoard or SwiftKey but more than good enough.

I really suggest you give it a try! I admit setting up the multilingual support is slightly convoluted compared to proprietary options, though. This comment was typed on Heliboard, et je peux facilement changer en français aussi and even avoir des sentences that changent between les deux without beaucoup de difficulté.

I use it for English and German. And it works great.

I use it for Spanish and it works perfectly, what language are you trying?

I had to stop using it for English even because its word predictions were horrible. Very common words kept correcting to much less common words on a regular basis. I gave it a good three months and I just can't do it. Wanted to like it so much.

Agree. And this is the first OSS keyboard I've found that can do multiple languages at the same time without switching the language/layout. (You can set secondary language) It requires a bit of setup (like downloading dictionaries) but I'd suggest to give it a try.