Two languages are used for any system level programming. The first one is Assembly language, and the second one is C/C. It does not matter what the operating system operating on top of the computer is, the underlying languages are the same. At least the language of C is the same. Assembly language has instructions that are specific to each chip. The Assembly language code understood by a Sun Sparc workstation will not be the same as the language understood that is understood by your laptop. Your cell phone’s Assembly language will understand a different form than either the Sun workstation or your laptop.You can find a quick rundown here

While Assembly is used, most of Linux is written in C/C. Every Linux version comes with the Gnu C compiler which operators can use to install new programs. Many Linux distributions come with their own package manager to reduce the need to run the compiler. A true Linux and Unix devotee will not use the package manager, but many people prefer something that they can download, install and just have it work. Not everyone is a master programmer.

C will always be an essential part of Linux. This will not change no matter how many package managers Red Hat, Ubuntu and Debian go through throughout the years.