Another vote for wide lenses. Most cities in Europe are pretty tight, so unless you're expecting to shoot wildlife or have a lot of time for scouting/shooting landscapes, I can't see a long lens being overly useful.
Depending on the type of shooting you're planning on doing, I'd almost be worried about 18mm not being wide enough, if anything. For casual photos it would be fine, but if you're looking to do any architecture or cityscape type stuff, you may run out of room.
I'd say just bring the 18-55mm and 12mm. If it were me, and if I was working with your setup, I'd get the 23mm f/2 and bring that and the 12mm, and that's it. But it seems like you prefer zooms, and you've already got the 18-55.
