Who invented the word "gonna"
The word gonna is referring to the verb phrase going to. It is originally a West Germanic language that came from England. The original construction involves physical movement with an intention, such as I am going (outside) to harvest the crop.
Idk, it was probably derived and used as slang from "going to". I know I use it.
It's just slang you can't really track that stuff down, except to nations or regions