На каком языке программирования написан движок Blender?

Цитата с сайта документации https://wiki.blender.org/wiki/Reference/FAQ
Blender Dev FAQ
What Language is Blender written in?

Short Answer C/C++/Python.

C - for Blender's [startup/main-loop/shutdown] and most internal functionality, tools, drawing, GUI and editors.
C++ -physics, audio, game-engine and Cycles render engine.
Python - The interface definitions, addons, most format import/export and some tools.

Why C/C++/Python?

Part of it is historic, part of it is convention and choice of the current developers.

Early on when Blender was developed, (1990's), C was very common for developing graphics applications (C++ compilers were expensive, where C compilers were free).

Python was selected because of its great community.

Nowadays Blenders core is still in C, some libraries are in C++, and OSX integration even uses Objective-C, Scripting is done in Python.

Currently this works fairly well and we don't have plans to rewrite large parts of Blender in some other languages.