if i would buy the first set in german (including all the adventure packs)
and then i decided to get for example wrath in english. do i have to use things from the first set?
or is everything completly seperated?
AFAIK, each of them is a complete game with no crossover content. You might of course, have to re-learn the terminology. But then, the ruleset varies a bit from one to the other anyway I think.