I left Microsoft on August 12th.
Microsoft's MSPaint is written in C++, as far as I know.
I am writing this in C#.
The reason the move to the ribbon destroyed mspaint was not because of the ribbon itself, but the fact that the ribbon is now the only way to access certain features. Many shortcut keys were removed (such as Ctrl + F for fullscreen) or reconfigured to less useful features (Such as Ctrl + R bringing up rulers instead of rotating an image, which now has no shortcut key), and some features were removed outright (Inverting colors, which was very
useful for many of the hacks I use in my mspaint tutorials such as the one I'm posting tonight).