Here are two ways of measuring programming language popularity:
- Rank by number of questions tagged with that language on Stack Overflow
- Rank by number of project on GitHub using that language
According to this article, these two measures are well correlated.
I’d be skeptical of either metric by itself. A large number of questions on a language could indicate that it’s poorly documented, for example, rather than popular. And GitHub projects may not representative. But the two measures give similar pictures of the programming language landscape, so together they have more credibility. On the other hand, both measures are probably biased in favor newer languages.