When Gibson's movie came out I went a-hootin' off to one of my learned friends and complained. He agreed with me and said that rumor had it that Mel went with Latin because of something to do with his relationship to the Church.
Now Mabel Freebucker from Dry Gulch spoke Latin, I'd stake my life.
Very true. I think here it's largely a matter of geography -- Europeans frequently can get along in more than one language, but it's a day trip or a weekend trip to another country, so there's plenty of opportunity to practice. I hear Japan is pretty monolingual too, what with the isolation.
My own Lithuanian grandmother also spoke Polish and Yiddish (no, she wasn't Jewish, but she was a shabbas goy as a child), and -- as she put it -- enough Russian so no one could sell her anything in it.
That being the case, it seems almost a certainty that being in Galilee, that close to the main route between Rome and the Near East (Syria, Babylon, etc), that Jesus spoke Koine Greek fluently (and could probably read and write it too). The Septuagint (Greek translation of the Old Testament done in Alexandria in the 2nd or 3rd century B.C., if my memory is correct) contains the majority of the passages quoted by Jesus, as well as the other disciples and Paul. This means they were all reading the Septuagint and were familiar with it.
So Jesus certainly spoke Aramaic, could probably speak, read and write Koine Greek, and could at least read and write Hebrew (but he probably spoke that, as well). I wouldn't say it's out of the question that Jesus could have known a good deal of Latin, too.