@michaa7: that is what he means, the GUI…
it's awkward and a pita, Mte90, but this will soon have an end, once the new forum is up and running. for now, adding &lang=en is faster than choosing English and finding the thread in the forum again…
here is a way to fix it: click on Profil, once you are there click on Postnuke Profil, then on Benutzerkonto, then on Sprache wechseln, choose English, save it, and pray xD