First off I would focus more on C++ and get familiar with it than try to make cheats.
I don't have any good source for C++ though but I bet there is a ton of videos on youtube. You could also check out Udemy.
And as for the best language to code cheats in is your personal opinion. If you are going to make a internal cheat for csgo a lot of people would say C++, but I do my cheat in C# since I am more familiar with it. It's a bit of work around to make a internal C# cheat but it works.