I've just stumbled over a great answer by Armen Tsirunyan, in which he used a large block of explanation in Russian. He then added a translation (a really amazing work I should say), but my question is: should we in general dis-encourage pasting long explanations in Russian, if the OP is in English? It seems to me to have little sense. I admit, for a foreigner who is learning Russian, it is already helpful to have an answer findable in English, even if the answer itself is in Russian. However it seems to me that we are relying too much on an obvious fast that most of us speaks Russian at the moment.
I guess it's absolutely acceptable and desirable to post the quotation. But whenever you do that you should also provide a translation or at least a summary of the gist.
In my book there are three important advantages of that:
Providing a Russian text gives the OP the opportunity to work through that text (without reading translation or summary first) and trying to figure out what it does say. Provided, of course, that he is able to read Russian texts. Then he can compare with the translation or summary. - In case of not knowing Russian and accordingly unable to read that text, the OP will jump over the part, but will not dislike that part.
It is more obvious that the answer is not based on personal opinion of the author of the answer (only), but that the content is provided by an external source. Provided that the source is known for reliability and the answer hopefully visibly pointing out what the source is, then it implicitly strengthens the validity of an answer.
Other people than the OP can figure out more quickly if the answer is good or not. That's necessary if they are not very familiar with the topic or they're unsure and therefore they are in need of external resources to make your own opinion about what the answer may be. If the quotation is missing they need to follow a link (if provided) and search the appropriate paragraph in the source.