I think I need someone to correct me if I am wrong.
1)This sentence means "We don't talk about such things!" I assume. "Such things we don't talk about!" is not proper English in this case.
2)But if it is intended to say "Such things we don't talk about!" as in "Hey, I saw XXX doing XXX this morning! He is so shameless!" "Shh, be quiet already! Such things we don't talk about!", it would be proper English.
So, which one is it exactly? 1) or 2)?
(Sorry for my strange speaking style.)
Seems the second one. It's my understanding that here they merge two sentences with the subject (vi) acting as a link, so is not repeated. Good thing of not being an English speaker is we can concentrate on how the sentences are built in Danish, instead of how it sounds in English or in our language. For me it helps to think in my own language in terms of ideas (what you want to say, generally speaking) and memorize the sentence as it is in the other. In daily life terms: when going to the supermarket in a foreign country, don't do currency conversion on each product, just learn the prices there ;)