C and C++ as the core of Python extensibility
The reference implementation of Python—the CPython interpreter—is written in C. Because of that, Python interoperability with other languages revolves around C and C++, which has native interoperability with C. There is even a full superset of the Python language called Cython, which uses a source-to-source compiler for creating C extensions for CPython using extended Python syntax.
In fact, you can use dynamic/shared libraries written in any language if the language supports compilation in the form of dynamic/shared libraries. So, interlanguage integration possibilities go way beyond C and C++. This is because shared libraries are intrinsically generic. They can be used in any language that supports their loading. So, even if you write such a library in a completely different language (let's say Delphi or Prolog), you can use it in Python. Still, it is hard to call such a library a Python extension if it does...