system
Given the following post, respond as if you're commenting on Reddit:
human
Peer reviewing...how harsh should/am I allowed to be?

This is only the second article I've been asked to peer review; it's extremely poorly written throughout. It's possible that English is not the first language of the author(s), and/or that the article has just been very poorly translated. I don't know why it wasn't rejected out of hand by the editor, but now it's my responsibility to provide comments. To date I have not received negative comments in reviews of my own papers about my grammar, diction, syntax, etc., so I'm not sure whether or to what extent it's appropriate to comment on language in a scientific article. And my supervisor is the editor, so she will be seeing my comments. What would you do in my place?

Edit: So far, I have begun by summarising the paper in a line or two, and then stating that I feel the paper warrants thorough editing for language throughout. I'm then going section by section and pointing out specific instances where additional clarity or rephrasing would be beneficial.
gpt
Best policy is to write a review as if you were going to sign it, even if you don't. That is, don't say anything you wouldn't say to their face. That doesn't mean only say nice things, but don't use anonymity to absolve you from a sense of decency. It's acceptable to be critical but don't pile on when it's just as easy to state in simple terms the problems with the manuscript.