Udo Rumpf wrote:

I would want to fly in up to a dozen countries.
I would like a European central office that would handle or answer
the questions.

There is no such thing as an European central office for gliders. Glider
regulations are strictly national.

That said, if your glider has an N registration and you have an US
license, I strongly believe that you can fly wherever you want without
any additional paper work. But you *will* need a liability insurance.
(Order of magnitude of 2 million Euros or something like this.)

Your best bet is really to contact the FOCAs of every country you want
to fly in. They tend to be helpful.

Stefan