I am reviewing a paper for a major journal with very high impact factor. Some of the authors are very well known in the field and have several other papers published in this particular journal, such that their objectives and results are likely valid ("likely" is the best you can get in this field, so don't get hung up on this). However, they are not native English speakers and the paper is almost completely unreadable.
Usually, I would immediately reject the paper. Due to their reputation, however, I forced myself to stay with the paper for a couple of weeks. From what I could understand after several attempts, their results might indeed have the potential to be published in this journal, but the editorial board is typically very strict: If I send a report claiming that the paper needs to be pretty much fully rewritten, they will likely reject it. I do need, however, a fully rewritten version even to be sure that I properly understood what they claim, and then to reinforce or change my mind about the paper's relevance.
I am thinking about sending a report where I state what I believe the paper is about, and if this is the case then it might be relevant, but I cannot be sure because it is currently unreadable. If the authors revise it, then I will be happy to read it again. The journal might still reject it, and I'd feel bad because this is essentially blaming people for not knowing English. I then wonder if there is any other way, e.g. contacting the editors directly instead of writing a report. Would this be better? Are there other options?