There was some of it found in Antarctica. I would assume that “vibranium” was just the English name of it, so the people of Wakanda using that term makes as much sense see their use of English in general (to the benefit of the audience.)

But even in the movie Klaw said that Wakandans called it “the gift”. So maybe their actual word for vibranium is whatever “the gift” is in Xhosa (the actual language used in he movie for Wakanda.) According to google translate that would be “isipho”...I wonder if that word appears in the film anywhere.