Why was Killmonger illiterate?

I'm supposed to believe that someone who can't string two words together correctly was a top CIA operative?

Here's a line from the comics:

"Yes, we were deadly foes! Yes, we strove, warrior against warrior, in battle! We would have killed each other, had fate decreed! But to see a valiant man like T'Challa cut down by the weapons of the West is too much. A death by foreign assassins is a death without honor!"

-Iron Man Annual #5

And here are typical lines from the movie:

"I'm gonna track down anyone who would even think about being loyal to you , and I'm gonna put they ass in the dirt"
"Wassup? All that challenge shit is over with . I'm da King now."

Is it just that Michael B. Jordan can't speak correctly? I remember in the first Creed movie Rocky says that Adonis has obviously been to college, based on how he speaks. It was ridiculous - Adonis was as illiterate as this Killmonger.