I started learning Japanese as I started using Heliboard, for now I just swap back when I need it. GBoard doesn’t play nice with the language button switching between apps so I just use the OS keyboard button and have the language button disabled everywhere, which also frees up some space!
Heliboard has swipe typing? Just go to the settings and tap on “Gesture Typing”. I believe you have to download a proprietary library for it, though.