Linux is written in a mix of programming languages. The Linux kernel, which is the core component of the Linux operating system, is primarily written in the C programming language. The reason for this is that C is a low-level language that allows for direct access to the system's memory and resources, making it well-suited for operating system development.
Additionally, some parts of the Linux kernel are also written in assembly language, which is a low-level language that is specific to a particular computer architecture. Assembly language is used for performance-critical parts of the kernel, such as the system call interface and the kernel's interrupt handling.
Also, Linux, as a whole is not just the kernel. It comes with user-space utilities, applications, shell and other tools which are written in different programming languages, like C++, Python, Shell, Perl, and many more.
So, Linux is a combination of many different languages, but C is the primary language used for the kernel.