A few, actually. The vehicle accessories drivetrain calculations are in Lua as are much of the game logic, the menu system is in HTML and Chromium (which itself is C++), the vehicle's jbeam is written in JSON, and the game engine (Torque3D) is mostly C and C# as I recall. The actual physics core I cannot say, but I think it's probably C or a sibling of it; I can't tell since it's compiled as part of the game.
I am to slow. Edit: Adding to what the guy above me said, The ui elements are written in Html and uses JavaScript as a middleman between the lua scripts and the HTML frontend. TIL, the CS files in the BeamNG Dir is not C#.
Most of the info posted here is near correct. C++/C for the game engine and physics core. Lua for scripting. JSON for serialization of data HTML + Javascript for interface/apps CS files are not C#. Is and old script language "console script" that is deprecated and will be removed when we have time
