Pointing out language mistakes in a review
If a reviewer has problems to follow the arguments and feels that this is due to the use of English, they usually include this in the review. Unfortunately, it is sometimes hard to pinpoint exactly what is unclear about the language, but a good reviewer should make some effort to help the authors. On the other hand, if the overall recommendation will be "reject" many reviewers do not invest the time to write down all unclear/wrong/misleading formulations. Note that a good reviewer may still follow your arguments although the language may be quite misleading (by just knowing what you are trying to show and correcting the wording while reading).

So you may ask for clarification (and I find this a reasonable request), but you should not expect to get an answer if the paper has been rejected anyway.