I remembered that the number of monthly questions for each language could be a nice indicator of the programming language popularity, at least here on stackoverflow. Would you consider to implement something like this?
The number of monthly questions for each language isn't really an indicator of programming language popularity. It doesn't take into account the difficulty of learning the language or the availability of proper documentation (and probably many other factors).
That being said, Sam Saffron (waffles) wrote a SEDE query recently that shows how many questions per month each tag in the top 10 tags gets. (Click on the Graph tab right above the results.)