Japanese keyboard is half-functional (edit: nevermind) (edit 2: undo the "nevermind")
Here is the 2nd issue, without solution so far.
Japanese keyboard sometimes only outputs hiragana with no way of converting to katakana and/or kanji.
And sometimes it does provide a way of converting to katakana and/or kanji, but no way of inputting it.
The arrow keys don't function, I guess that's WIP?
The 記号 key simply outputs "記号" (if conversion doesn't work) just like on Ubuntu Touch, should switch to symbol picker.
And the 戻す key simply outputs "戻す", which 1) it should read "戻る", and 2) should close the keyboard (currently you swipe the keyboard down to close it, so perhaps it's unnecessary altogether?).
For the ones curious about the difference between 戻す and 戻る, the former means "to give back an item to someone", while the latter means "to go back to the previous part".
The conversion should work, it looks a suspiciously lot like what you see in Ubuntu Touch, and I'll try to debug it myself along the way.
The other things I assume is still a WIP.
Edit:
Found the solution to this:
export QT_IM_MODULE=Maliit
export GTK_IM_MODULE=Maliit
And this fixed the arrow keys at the same time.
Edit 2:
This solution is no longer working.