Not really hidden, though. Often Linux distros even have gcc preinstalled.
Will it stay around? Yes, because it allows writing performant software as our CPUs and compilers are made for it and performance does matter very often.
On the other hand, Rust is being used even in the Linux kernel now. It lets you do the same things as C, so the only thing holding it back right now are the lack of some more exotic C extensions like guaranteed tail calls / computed goto.
For an actually hidden language, try Mercury. It is not famous or widely used and its tooling is not quick to get started with. However, it will definitely broaden your horizons much more than C, which is similar to all the mainstream languages.
Agreed except for R. That language’s documentation and semantics are painful. Not Malbolge but reminds me of PHP and BASICs with weird limitations.