Number of Classes / Functions (or "Size" to be more general) in the Standard-Libary. Most Languages come with such a thing. LiteC has built-in, specific functions, C has its stdlib, Java the Java-Class-Libary, C# the .NET-Class Liabry, and so on.
It differs on many Languages. Of course, the problem could be how to measure it (classes contains often more logic than single function, and what is part of the "official" bundled libary?). And to get to values could be also difficult...

But maybe an option for you ("popularity" can also just be estimated)