I propose to write ñ instead of ng' and dy instead of j except nj !
Example is attached.
I think that trigraph ng' was used just because of English keyboard and j except nj is just remaining of arabic script.
Swahili is not an African indigenous language because it is a lingua-franca by itself (e.g. English is not a lingua-franca by itself...) so Swahili has World-wide sense!