So say you are writing a review which includes paper A, which claims to introduce a new idea to your field. In the course of reading surrounding literature, you find earlier paper B, which puts forward a very similar idea. Paper B is not cited by paper A. Normally the thing to do would be to add a note saying the paper B offered a similar idea some years earlier, then synthesise the discussion in both.
The catch here is that paper B is pretty idiosyncratic. It makes various claims that contradict the established wisdom, and does not (in my opinion) sufficiently back them up. It is a long paper, but contains no numerical analysis, which on this topic is a bit unusual. It contains sentences such as;
What may appear as fancy mathematical formulations is primarily intended as an invitation to mathematical physicists to fill in the remaining gaps.
(Which, if you are minded to, is probably sufficient to find the paper I'm referring to.) It has been cited (by reputable papers) as a a publication, multiple times.
Is it reasonable to just mention this papers existence in passing, without really commenting on its odd nature?
Edit; the advice of a commentator helped me find the publication in question. It's not in Russian, it's in English, I just failed to find it before. It's not a lot changed from the preprint, and I still don't feel comfortable making a strong statement about the accuracy of its claims. The discussion of errors in particular seems to miss key aspects, but clearly at least one referee did not agree with that assessment. So it's quite possible that I'm missing the point.
So far I'm inclined to go with @Captain Emacs' suggestion, and possibly also email the author (politely) to see if they are willing to clear up my confusion.