Does G translate articles to foreign languages?

Yeah i guess so. thing about other language than english is that if you place the language according to your native one on your website chances of getting crawled using your keyword in german will be lesser. But i don't see anything wrong in commenting on the same niche even though its not on the same language. It is still related.

Issue here is about your keyword getting crawled. I suggest you use your german keyword as the username when doing a commenting.

it's hard to say whether G translates articles to make sure it's on the same subject, though G states in it's blog that translated content from one language to the other does not count as duplicate content

big G does translate but the trasnlation is always a little off since many words and or phrases are transliterates and stuff gets lost in translation...

I do have wp site with google translator plugin installed. I was amazed to find out that even translated posts were indexed by google. Doing this, my site is ranking from other local google searches, resulting to more traffic..