Can I, as a reviewer, tell authors to get a native English speaker to proofread their paper? I am reviewing a paper for possible publication in a respected journal. The English in the paper is very poor. The authors are clearly not native English speakers. I want to write something to the effect of the following in my review.


I advise the authors to find a native English speaker to proofread the manuscript.
 

My question: Is this appropriate in a review?

On one hand, I think it is good, constructive advice. The paper would be significantly clearer if someone spent a few hours helping them fix it up. I can try to help them through reviewer comments, but it would be much easier if someone could help them in person. The authors are located in a western English-speaking country, so they should be able to find someone.

On the other hand, I don't want to be "the mean reviewer." I understand that English can be difficult to master for immigrants. Perhaps there is a more diplomatic way of saying this.
It's obviously appropriate and constructive to comment on writing issues that significantly affect the quality of the paper. The only question is how to do it as constructively as possible.

Personally, I prefer to suggest that "the authors get editing help from someone with full professional proficiency in English" rather than asking for "a native English speaker." I see other reviewers write the latter, so it's not uncommon, but I feel like it sounds a little bit like I'm "punishing" the authors for not having been born in an English-speaking country. There are plenty of academics who are not native English speakers, and don't have the same proficiency as native English speakers, but are still perfectly capable of high-quality academic writing.