Should I do anything about a recent article in a respected math journal that is not up to its usual standards?
You could consider "doing something about it" if the article was indeed questionable in terms of its science,  i.e., if the data seems fabricated or you find faults in the proofs. Finding that this article's contribution is not exciting  enough or minor language issues almost certainly do not qualify. How substantial the results of a given paper are is rather vague and subjective, and spelling errors almost certainly are not grounds for retraction. The best you can hope for, in my mind, is a corrigendum of the spelling errors.

You should also keep in mind how your supplemental arguments will appear to an outsider:


  the authors of the paper are from country X, and the paper was communicated by a person from country X as well


First of all, this is not "suspicious" as it happens all the time. Further, and this is the big concern,
replace "country X" with "the United States", and see if you would still find this suspicious. With concerns like that, it is very easy to be perceived as judgemental or downright racist, so I would be extremely cautious in following this line of argumentation any further.


  the whole process (from "received" to "received in revised form") is only 3 months, and I wonder if enough time has been given to review the paper.


We all know that the review process is capricious. While 3 months is certainly well below my average review time, it's not outrageous to assume that the paper had the usual number of reviewers, all the reviews were returned reasonably quickly (in one to two months) and found the paper acceptable, and the authors only had to do minor changes for the revision. While most manuscripts don't go through as easily, this does not appear particularly suspicious either.