The French books

Yes, there was something very furtive and unexplained about those scenes. It seems as if Joey and Vlad were trying to improve their French before the school trip to Paris. Why steal them from the library, if that's what happened? Why not just check them out? Or was there something deeper going on?

Yes, they weren't even naughty books. They mentioned one of the titles was "Cyrano de Bergerac."

Just a theory, but it's the only thing I can think of by connecting dots provided in the film: It might all be subtly related to the girl. Joey told Uncle Ben about the time in St Croix that he fell in love with the windsurfing girl but never said "hello" to her. He somehow knew, however, that she and her family lived in New York and he might run into her, but still doesn't know what he would say. I'd like to think that he was studying French -- and appropriately, Cyrano de Bergerac -- to possibly woo the girl. Vlad was shown as having much more confidence (the early scene where he chats with Eugenia), so maybe he was helping Joey out. Since time passes in skips and jumps we can assume that it worked, and that she's the girl with him at the very end.