Mostly C. While C++ is easier to write, for very low level code, it is harder to maintain when you need to understand all of the side effects to maintain code

Mostly C. While C++ is easier to write, for very low level code, it is harder to maintain when you need to understand all of the side effects to maintain code safety. C++ compiler support is also sometimes not available. (And of course it's very like there'll be no Rust compiler available either in this case.)