"Programs must be written for people to read, and only incidentally for machines to execute." - Abelson & Sussman, SICP, preface to the first edition
There are almost infinite ways to write an application for GNU/Linux system. You can choose any of one stack and then create an application for GNU/Linux system. For example, if you are using GNU/Linux system with KDE then you can use C++ or if you are using GNU/Linux system with GNOME then you have many options such as C, C++, Python, JavaScript, PHP and few more. You might use electron (Please be mercy on your memory and don’t use it).
But GNOME strongly support C language. Because, GNOME itself is written in C. For the other languages GNOME give binding to use. But, there are two languages - Vala and Genie which have strong support like C for GNOME because both languages are developed by GNOME