What programming language is Stuxnet written in?

According to some analysis, Stuxnet was written "was written in multiple languages, including C, C++ and other object-oriented languages." Source code is not available, but binaries can be found in the right places. You can try Googling around. I suggest confirming the hash with a reputable site.

The Stuxnet dropper and payload were almost certainly written in C, based on the reverse engineering that has been done.

The payload inserts itself between the PC used to monitor the Natanz centrifuge array and the target centrifuge array. A classic 'man in the middle' attack.

Stuxnet injects Siemens PCS7 language malware into motor controllers to control the target centrifuge controllers. While the attacks are in process Stuxnet 'plays back' normal readings to the Siemens monitor software running on Windows.

The Stuxnet team certainly had experts both in Windows and Siemens controller internals.

Some functions called by Stuxnet have not been positively identified.

The Wikipedia article on Stuxnet lists many useful references.

Given that nobody is 100% certain who wrote Stuxnet, I find it hard to believe that anyone has found the source code for it.

Given the nature of its inner workings, it likely wasn’t written using a high-level language — especially a high-level language that is easily reverse-engineered. It’s probably written in C/C++ (well, those are high-level), but most of it is probably written in assembly.