So, this is a new one.....
In the interest of accuracy, how should this question be flagged? It's my understanding that StackOverflow is an English website, and that multi-language support was canned as not feasible.
I normally vote to close these as too localized.
As for flagging - if you feel the need to flag, then this would be an "Other" flag explaining to the moderators that the post is not in English.
There is no point in voting "Off-topic" for migration as if this will normally end up on another Stack Exchange site where chances are it will get closed pretty quickly (unless it is happens to belong, though for most questions asked in a language that is not English, this is unlikely).
If you do have the language skills to translate the question to English, that would probably be best, even if it does end up migrated to another site.
I would flag (or vote to close) as "Off Topic", since part of the parameters of what can be discussed on Stack Overflow requires the post be in English.
I have always thought non-english questions should use a language tag. I n this case:
[DE] and the have the users ignoring languages different then theirs.
But that was long discussed and rejected :)