99% of all high performance games are written in c/c++ so yes, the 3D engine is written in that. However, MG seems to have continued the tradition of writing the GUI in an "easier" language so that is written in C# this time (it was Java in IL2). Many other games have the same approach as C# is a much nicer language to write GUI:s in.
In the background of some image from the MG office taken a year or two ago I remember seeing something that looked like collision detection code written in C#... That must have been something else though, if they are mixing c++ and c# in the 3d engine they sure would get problems with performance... No conspiracy theories now please
