ok, my german is sorely lacking but I think what you're asking about is the battle tower before you take over it. What you have to do is
get the soul forge contract from the chest in the Erlking's room. I believe it's(the key) in an undead that you must kill on a lower level in the tower. The Goblin will never speak, though you can read his books if you've done the appropriate mind reads prior to getting here.
Hope that helps, I can barely read German and can't speak it myself at all. Maybe someone more fluent will help if I'm wrong
