For the nrc_makah keyboard, I have a key ƛ̓ (U+019B LATIN SMALL LETTER LAMBDA WITH STROKE followed by U+0313 COMBINING COMMA ABOVE). However, the combining charater renders poorly in the default font used in Keyman for Android (and I presume Keyman for iPhone). Namely, the COMBINING COMMA ABOVE renders at the top of «ƛ» rather than above it, making it an indistinguishable mess. On my Macbook, system Arial renders this acceptably. I have set the font in the .keyman-touch-layout to Arial, however I see no difference in the font (see screenshot).
Follow-up question: is the "font" entry in .keyman-touch-layout officially supported? I had assumed this was the place to change the touch keyboards font but I can’t seem to get it to do anything.
This is now only used in development, not in deployed keyboards. For deployed keyboards, the font entries in the package are definitive. I think we still need to do more work here, but it’s hard to know exactly how to solve this.