Answer 1

Github has a section where you can see different Game engines. There you will see what language they use and also other details.

If you want something simpler (like a bookstore) I would recommend using Gosu. I've worked with the bookstore in Ruby and it's been a lot of fun, and the projects I've seen in C++ seem to share the same development mechanics.

https://github.com/collections/game-engines
https://www.libgosu.org/cpp.html