Good idea, maybe something like the number of code lines. That would value bigger projects higher then small projects. Which actually make sense to me. Because small projects are probably written in a specific language for a reason: batch files, css, html, examples, tests. Whereas I am interested in what language people choose for bigger projects, where several languages could used but still one has to be chosen.

It would also make sense to weight in the date a project started. Newer (big) projects would then weight higher then older (big) projects.

So I think taking in account the number of lines and age together is a good way to really visualize trends.