I recently answered a question on SF.stackexchange; the story which required identification was originally written in Italian and seems to have never been translated to English. However, it was translated to French, and this is the version I had and that the person who asked the question was looking for.
Since SF.SE is English-speaking, should I try and translate (even approximately) the quotes, or leave it in French and have people take my word that it is the right story?
In the general case I would say it is usually preferable to translate the quotes, even if it is just using an online service. However, when doing so (and this is a practice I've seen done around the site) you should leave the quote from the original language and include the translated one too. That way it helps everyone and people can spot mistakes in the translation if necessary.
I think though generally it should be treated on a case by case basis. A lot of times what makes sense in one question/answer doesn't make sense in another.
You might want to look up these questions for further reading:
In this specific case I don't think it is entirely needed. story-identification questions are a bit of a special case in that they only really exist to help the user who asked the question whereas most questions and answers on the site are more applicable to the larger audience.
In this case as well, as you mention, the OP was looking for the French translation of the work so arguably the French quotes are better here than the English translations.
Further, for a story-identification question the most important part of an answer is that it includes the work name. Sure, it wouldn't be a good answer if it only included the work name but it would still be an answer to the question. As such any further effort is mainly secondary, even if pretty much mandatory.
So, you could go to the effort of translating the quotes and including them but I don't think it is entirely necessary in this specific case.
You should translate. Both for the sake of future non-bilingual readers, AND as another comment noted, for search purposes.
You should also make it clear the methodology for translation - is it copy from officially translated work? Your personal translation as a biligual person? Google Translate without fixing? This way the reader can gauge the quality of translation.
Personally for Russian stuff I tend to try to do high quality idiomatic translation, when I have the time - you can see examples in [night-watch] tags.
