>>> if you haven't read it in French, how can you comment on the quality of the translation into English?
I think that it's sometimes easy to spot failings in a translated work even though you've not read the original. For example, when I read Mark Adrian Corner's translation of Zdeněk Jirotka's 'Saturnin', there were points in the story where it seemed readily apparent to me that Corner had opted for a very literal translation, thus leading to a rather stilted style in places. I didn't need to have read the original Czech version to form my opinion. (It's still an interesting read though:
https://www.goodreads.com/book/show/1724928.Saturnin ).
With regard to the ending (or various possible endings) of 'Histoire d'O', which I've not read and I doubt would appeal to me, there's some relevant info on Wikipedia which might be of interest to you:
https://en.wikipedia.org/wiki/Story_of_O