Chinook Jargon’s /yaka/ indicates pidginization from Chinookan /yax̣ka/
Now an ultra-short note.
Image credit: How to Pronounce
Chinook Jargon’s 3rd-person singular animate personal pronoun yaka ‘(s)he’ (and sometimes ‘they’) is a simplified version of its etymological source, Clatsop-Shoalwater Lower Chinookan yax̣ka.
Because pidginization!
Prove me wrong.

