I write in two languages several times throughout the day, and worse: I code-switch all the time between the two (in the same text, that is).

That is definitely the killer feature for me. So I have an old version of swiftkey, blocked Internet access because fuck me if I let Microsoft snoop on all I write, and an xposed module (Exi) with useful mods.

PS: if anyone has a Free Software alternative I'm all ears.