very nice question I believe, what I personally do is to send seller a PM spotting the translation error and ask him friendly to make it clear to bidders about the mistake, I believe all people here are honest enough and would clear it in the thread for bidders, if the seller won't respond and/or keep the wrong description without making it clear in thread, I'd PM a moderator and explain the situation and ask for his permission first to post on that thread, fair enough for everyone I believe
The worst scenario in my opinion is when you find some native post the wrong translation and/or description, I'd call it a pure SCAM, I'd PM a friendly message first, keep an eye on him, if repeated, I'd call a mod and ask for an action against, after all, we remain a small community built on transparency and honesty, if missed, it'd be a mess!