I have been given my first manuscript to review for a journal. The topic is a very good one, it fills a research gap nicely and is an area that I specialise in. However, the execution of the paper is lacking. I am about halfway through making comments on it. The English is consistently poor in both spelling and grammar, and the structure is dire, which makes it hard to follow the main arguments. I am aware that bad English is no reason to reject a paper, but the English in this paper is very confused in many places, sometimes multiple times per paragraph, and it's a trial to follow.
I believe that the paper could only be salvageable after a rewrite, but by a third party. I don't believe the author's English is good enough to bring it up to standard. I do not care about being 'kind' to the author, but the topic is so good that I would love to see it go through, but I am torn between accepting it with majors or recommending rejection. My PhD supervisor has advised me to recommend rejection, but I am still unsure which way to go. Should I recommend acceptance after major revisions in the hope that it will improve based on my [now extensive] advice or just recommend rejection?