People usually pronounce proper names differently than the origin-language pronunciation for a couple of reasons
- they don’t know the origin language, so they pronounce it based on the pronunciation rules from their own language, or
- the person with the name has decided on a preferred pronunciation and those who know that person use that pronunciation.
Xavier came from the Basque language. It was originally a place name that evolved into a family name. In Basque, the X sounds like /sh/. The V probably sounded more like a B.
It’s easy to see how this Basque pronunciation evolved into the Spanish version: ‘Javier’.
But how did it come to be pronounced “X”-avier?
Maybe its part of an ‘anglocentric’ approach to non-English words (reason #1 above). In English, if you see an X, you pronounce it, either as a /ks/ or a /z/ sound. English has few words that begin with x, so when confronted with this new pronunciation challenge, maybe they guessed what it might sound like. Regarding mispronounced names, I know from experience that after a while, you just stop correcting people about how to pronounce your name and go with whatever they say, especially if everyone is mispronouncing it the same way.
Or maybe it’s reason #2 and this idea is more fun! Maybe someone just thought it would sound cool, tried it, and it caught on with other people. Or maybe X-avier came along after the X-men comic books and movies were published, and it became a popular new, cool pronunciation of a name that was previously difficult to say ( Javier or Xavier). Difficult for non-Basque, non-Spanish speakers, that is….
Personally, I would like it very much if people thought about super heroes every time they said my name!
Note: We have a young friend, 12 yrs old, named Xavier. He’s from a Hispanic family. He calls himself “X”. My grandsons think his name is very cool.