Include libraries in other languages in a C application

My general question is this: what's the most common way to include libraries in other languages in a C application?

For example, if I have a Ruby library intended for doing function X, and a Python library for doing function Y, how can I write a program in C (the language, that is) that uses the functions in each?

I've seen wrappers that give access to C libraries in these higher languages, but are there wrappers that go the other way? Is there a common way of handling this in general?