I think it's like proofreading - there's a big fat gray area. We don't want the site to become a free translation and/or writing service. We want answers to be useful to more than just the person that asked the question, so that we can build up a library of answers catalogued by the questions they answer.
If I ask "is this sentence correct?" (whether it is a translation or just something I wrote), the answer is probably not going to be that useful to other people.
Example of translation questions that only help the translator:
Translated text about Royal Baby
If I say "I wrote this sentence, but I'm not sure if I should write 'your next meeting' or 'the next meeting' - that might be a question that someone else has and could find on the site. Or, if I say "there is this expression in my native language - what is the closest equivalent in English?" and then proceed to explain the phrase in English I think that's useful to other learners as well (even if they don't speak the same language natively that I do).
Example of translation questions that may be helpful to other learners:
French --> English "À leur tour" or
How do you say "patio de vecinos" in English?
I would just flag questions as "should be closed" if you come across one you feel strongly about. At 3000 reputation you should be able to vote to close directly. I usually use the off-topic/other and leave a comment explaining why.