The word derivation of "Christmas" (= "Christ" + "Mass" [as in Catholic]) is, I think, almost exclusive to the English language. It's ironic that the Romance languages themselves use a term which does not reference Catholic doctrine but rather is analogous to "nativity" ("Noel," "Navidad," etc.), whereas the Protestant Anglican church calls it "Christmas."
Merry Nativity (or whatever you choose to call it)!
Duh, I went to the 350 languages site and there are more variations of the word "Christmas" represented than I realized. I don't know how many of those borrow from English, but still, pulling foot out of mouth...