[krapht]

Are you trying to become a systems programmer? Then you need to know C and C++, period. And not just C and C++, but also the surrounding ecosystem like CMake, Make, Autoconf, GoogleTest, Catch2, Python, Qt5, Boost, etc. Unless you are fortunate enough to work at a place doing completely new development, the programs you will work on are written in C/C++. Knowing a language isn't just knowing the syntax, but also the libraries, scripting, and build tools.

If this is for fun / education then learn Rust. It's conceptually nicer and doesn't have legacy cruft from decades of industrial use.