Why do the Wakandans speak English?

Question

In the MCU, the inhabitants of the nation of Wakanda largely speak English (although other languages, such as Xhosa, Zulu, and Igbo, are also heard). It's not simply that they are cosmopolitan and happen to know English: this is the case even when people are speaking among themselves, not foreigners. That said, in real life, countries where English is the dominant everyday language tend to be either the UK or former colonies of the UK, for obvious reasons. Wakanda was highly insular, never colonized, and quite independently wealthy, which would seem to disfavor most reasons to adopt English as an everyday language.

Obviously, out-of-universe, most of the actors were American, and most American audiences would not understand the other Wakandan languages (to say nothing of a conlang). However, in-universe, why is English the predominant language in Wakanda?

Answer 1

They aren't speaking English, they're speaking Wakandan, as confirmed in this interview with Entertainment Weekly. We're hearing them in English because it's convenient for the audience not to have to read subtitles and for the actors not to have to speak extensively in an unfamiliar language. This is referred to in films as a 'translation convention'.

Apart from a handful of terms, T’Challa’s fictional African nation had no differentiated language in the Marvel canon. But its people wouldn’t exactly be speaking English, since part of Wakanda’s lore was that the technologically advanced land had never been conquered.

Chadwick Boseman’s character does speak English throughout the movie to other English-speakers, of course. He’s a statesman, and presumably knows many other languages, too. But for intimate scenes between T’Challa, the prince of Wakanda, and his father, King T’Chaka, directors Joe and Anthony Russo felt the two men should communicate in a native tongue, one that rose up from the continent itself, free of interference from outsiders.

“The language we used for Wakandan is called Xhosa,” Joe Russo tells EW. “John Kani, the actor who plays T’Challa’s father in the movie, speaks the language and taught it to Chadwick. It’s spoken by 7.6 million people in South Africa.”

_{^{Black Panther language: Where Captain America: Civil War found the words of Wakanda}}