One Nigerian student when I was in college had a bit of an accent from the old country, but it was still British English, with Britishisms (a flashlight was a torch). When he ran into an urban black in the neighborhood who talked jive, he switched to perfect BBC English, and you could hear the contempt. He was an engineering student, and did quite well.
LOL
https://www.youtube.com/watch?v=GgZYCj39M38
A video of a REALLY funny comedian named Trevor Noah. Black guy from South Africa. The entire thing is really funny, but he goes into his bit about learning to be an American Black at about 2:15.