A friend of mine - an accomplished writer in his own right - recently asked my advice about writing a review of a translated book. He had compared the translation with the original at certain points (how wonderful that he was able to do so!) and had questions about some of the choices the translator had made though he thought the translation was very good overall. He wanted to know if I thought he should discuss these quibbles in his review. Since I think this same question must come up for a lot of reviewers of translations, I'll share my response:
Hey there, it's a really good question - I've written about this on my translation blog and recently co-authored a page of guidelines for reviewers of translations along with Edith Grossman and Jonathan Cohen.
I would encourage you not to try to compete with the translator in terms of linguistic expertise (let's assume he knows the original language better than you do) or complain about the "mistranslation" of individual words, because if there's a more obvious translation for any one of them, he surely knew that and nonetheless made an informed choice to do something different - though you might decide that the results of this informed choice are something you think isn't effective in English or doesn't sound like the author as you understand his voice, and these are things that would be really good to write about. If you think the translation is basically good, do these bits stick out like a sore thumb? Or is the translator trying something daring that isn't quite working? If you like the translation for the most part, what do you like about it? It's really great that you want to write specifically about the translation when you review the book. That's so useful, and there are so many things you can say about it without turning into the translation police. I hate reviews in which a critic declares a translation bad because it doesn't render word X with word Y - believe me, if you think of word Y, the translator probably thought of it too, so the real question is: why did he decide not to use it, and was that a choice that panned out well in the context of what he is doing in the translation as a whole? Think of the translator as someone possessed, like yourself, of a critical and aesthetic intelligence and engage him on that level, and you're guaranteed to come up with an interesting assessment of his work.