The VN was made in Renpy.
Ren'Py uses its own custom script, which to my knowledge is just called Ren'Py. I think it is just Python with a custom interpreter, but I'm not sure. Either way, you can execute Python code within Ren'Py scripts so a Python background could be helpful here.
Fortunately, both Ren'Py and Python are super easy to learn, so if you start trying to write a novel with Ren'Py you can learn both as you go.