Google's interface language
But first things first. The whole story started when I downloaded the german version of Mozilla Firefox since a mixed language interface sucks ;) Well, this comes with the german version of Google as default search engine which wouldn't be really a problem if this would only result in a german interface and not also in prioritisizing of german hits.
Well, now I also switched the google interface to English and suddenly google works again :-? Perhaps someone should explain them, that the interface language shouldn't have anything to do with the result set language.