[FreeFull]

There's nothing that forces a Wayland compositor to be written in C. I've seen ones written in C++, Zig, and Rust, but you could really use any language as long as you can still call the appropriate system/kernel APIs

[welterde]

Nothing preventing you from writing a X11 server in something else either (and people have done so!). But fact is, most wayland compositors right now are either pure C or C++ (and I think the rest uses at least wlroots?). Many X11 window managers are written in non-c languages too and I don't think I am too far off the mark when I say that a decent fraction of wayland compositors would just be external window managers if there existed a standardized interface for window managers when they were written (I think some compositors have an interface for external window managers now, but is there a standard interface by now?).