How to change functionality of backspace key

[JRBros2346]

I implemented Klingon quja' keyboard layout in Unexpected Keyboard, source code below vvv

This does not have a lot of symbols (I don't know the standard for placing symbols and i have just placed "some " useful ones randomly"). The problem is some characters are multi glyphs long like tlh and ng, but backspace only deletes the last glyph for example tl and n. How to change this behaviour? Google Board does this. Also, how to change keyboard font, because I and l look same