I think language popularity falls into two different categories: (1) languages other people will pay you to work in, and (2) languages that you would work in of

I think language popularity falls into two different categories: (1) languages other people will pay you to work in, and (2) languages that you would work in of your own choice. For #1, I would measure the frequency that a language appears in job ads. For #2, I think the trending repositories in Github would be a better metric than commit lines.