The name has nothing to do with Go the language; Just coincidence. It was taken from a play called Waiting for Godot.[0]
Internally, everything is C++ (and your code can also be written in it), but the bundled scripting language is called GDScript (it’s a bit of a mixture of Python, Lua, and others with some extra unique syntax sugar). However, it does support bindings to other languages. The most common being C# (using Mono), but people have gotten Rust to work (among others).