First thanks for your work!
I don't know if your keyboard is still maintained but I have a few bugs to report. I installed the keyboard using the ZIP on my Xiaomi mi4 with official MiUI developer ROM and except the following bugs it works fine
1) The popup for the currently typed key displays the corresponding character in a much too big size, so that the character cannot fit inside the popup
2) I enabled 2 languages (French and English US); when I switch from English US to French, the space bar displays "English UK" instead of French (though while swapping from one to another I see " French English US ")
3) Like sigma99, van oma and Mirsaneli, the keyboard "minimizes" when I press "?123" key
4) The height of the keys and the vertical padding between the keys are much higher than on your screenshots (hence lots of vertical space is lost)
5) I activated XT9 predictive text and ensured "Word completion", "Spell correction" and "Next word prediction" were checked; however, I don't have any word prediction nor correction (there's not even the area where the suggestions should be displayed). I know there's no suggestion area on your screenshots as well, but you said predictive text was enabled in post #35!
Finally, one feature that would be awesome: like on the stock keyboard, when you switch from English to French, the keyboard switches from qwerty to azerty. I know this might be tricky but it would be awesome