I like
Nicholas Peters' suggestion that it is derived from "Javier/Xavier" from Spanish. If it is indeed correct that the character is of Asturian origin, that would make sense! Incidentally,
Xavier comes from the Basque name meaning "new house" (etxea barria). I have absolutely no evidence of this, and it is probably wrong, but it just occurred to me that it might be a French adaptation of the Arabic name
Jafar.
"
Ja'far (Arabic: جَعْفَر), meaning in Arabic "small stream/rivulet/creek"
If he is Asturian, I would bet more strongly on
Javier, since Asturias is quite close to Pais
Vasco (Basque Country), but if his Spanish origins are considered in the context of "Fortune-tellers' son," as in the musical, I get a little bit of a sense of Gitano (Spanish Gypsies), which could have a much stronger connection to Moorish names. I don't know, but I am excited to see this conversation evolve!