I know it was a bit stupid, but I wanted a custom view of tags in the tracklist view. I started by cleaning all up by deleting all tags shown and accidentally pressed "OK" in that condition.
Result is that I can't start the application without it crashing immediately with some German error message (I have selected to install an english app).
I tried uninstalling and during uninstallation I selected to remove all application data as well, but that does not even help when I try to reinstall! I am lost now, how can I restore to default settings?