From what I learned about the Unifon alphabet, it seems
special non-ASCII characters used in the Unifon alphabet have been assigned code points in one of the Private User Areas…
Keyman Developer requires characters that are included in the Unicode standard (not private-use), and you’d also need a font to create the keyboard layout.
Correction: Keyman Developer does handle Private-Use Areas (PUA) characters, so you would just need to include the font with your layout.
If it uses a lot of Private Use codepoint it would need to be put in the
experimental section rather than