All posts returned are in English, the default language. The posts should be in the current language, in this case German. (Note that the permalinks appear to be in the correct language.)
I guess WordPress sucks in this. Not sure how that data is requested but from get_terms() you can't modify the taxonomy names. No clue yet how other plugins doing this.
For example: http://freespeechdebate.com/de/tag/christianity/
All posts returned are in English, the default language. The posts should be in the current language, in this case German. (Note that the permalinks appear to be in the correct language.)