It's somewhat of an antijoke. Translation would be:

Two camels are sitting in a cellar chopping petroleum. One of them says: "Tomorrow is Christmas, you know?". The other one replies: "Yeah, I came here by bike anyways"

The whole joke is based on subverting expectations. You don't expect camels sitting in a cellar, a liquid can't be chopped, camels can't speak (and wouldn't care about christmas either), camels don't ride bikes, and noone chooses a bike as a mode of travel especially in expectation of Christmas.

I personally never found it that funny, but my mother was laughing as if it were the funniest thing ever said.