In the past, Hausa and Zulu have been used in the comics, while Xhosa is used in the movies.
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Zulu’s not spoken near where Wakanda is supposed to be. Hausa’s a stretch, but Wakandan could be a relative. Xhosa was used for the movies as the actor who played Tchaka is a native speaker, though adding a few words from languages of the area would have made sense ( take a word for metal and make it mean Vibranium, for example). Really, the reason for making its own language is because Marvel already got the linguist who created Dothraki to make Dark Elvish in Thor 2.