Thanks for raising this issue, Moin! While you are talking about the German translation, I think it makes sense to raise this also in Add 'stop impersonating' link to user avatar dropdown when impersonating - #41 by ted where changes to the feature are being talked about.
In my personal opinion, the fact that “impersonation” doesn’t translate well is a case for changing how the feature is named. I like “log in as user”. I also can imagine “Switch to @impersonated_user account” and then “Switch back to @my_account”. I think this works in english and also suspect it translates better into most languages.