Well I'd say don't go over the top, but don't be afraid to wear something smart. After all, if others choose to dress down - their loss.

I'm just a little confused though - you say you normally wear a black dress - to a wedding? I would have thought that would be a bit of a no-no, at least in the anglo-saxon world? Save the black for a funeral. But who knows, Swiss or Germans might think it is totally normal to wear black to a wedding - not sure on that one.

Went to a Swiss wedding the other week. Normally I would wear a suit to the wedding just out of respect, but nobody did. Mind you it was a baking hot day, and we were all outside. Some people turned up in shorts, but I made the effort to wear long trousers and a long sleeved shirt (rolled up). Some others did as well, but not everybody. I think it would also be highly dependent on the bride and groom as to what they might expect. Do you know any of the other guests? Why not ask for their opinion?