The people of Wakanda in Black Panther spoke with an accent. Was it invented for the movie, or is it from a particular part of the world? It sounds distinctly African, but I can't pinpoint a country or region.
From State.com (emphasis mine):
Beth McGuire: Visually, that’s where we were. Linguistically, what we did is we honored the genealogy of the precursor to Black Panther—Captain America: Civil War. T’Challa’s father, T’Chaka, played by John Kani, is in the previous film. John Kani is from South Africa and he’s Xhosa, and he’s playing the king of Wakanda. So, Ryan and I went back-and-forth and talked about it, and I said it just makes sense. If that’s who you started with, that’s your king of Wakanda, that’s who it is, that’s the language. And so we did. We chose Xhosa, and it’s a very challenging accent, but it was kind of the kosher thing to do if we’re going to look at the genealogy of who they started with in the Marvel story. What was interesting, also, was that the young T’Chaka is played by John Kani’s real son, Atandwa Kani, in real life.
So they picked the accent associated with the actor's real-life ethnicity/national heritage, to be particular the Xhosa people's accent.
Note: Beth McGuire is dialect coach in Black Panther