Cogmind is written in C++ (as is REXPaint--same engine). I've talked about just about every aspect of development on the
dev blog, and also in
r/roguelikedev FAQ Friday posts. I talked a bit about the language/library choices in
the first one, though technically you can use any language to create a roguelike.
r/roguelikedev is definitely the place to be if you're looking into working on a roguelike in particular (though it sounds like maybe you're not--just ASCII). (I do plan to one day write an introduction on how to get started with roguelike development, as well as cover (on the blog) some of the more basic architectural components of Cogmind and the engine.)
Can I copy designs from RexPaint into a word document?
Sure, you just press ctrl-t to export an image to a text file and can copy it into a Word document, although as text it won't retain color information... To get color info into a Word doc you'd have to write a converter from one of the other color-including export methods. (But why would you want to use Word? It's not a good approach for art. Or maybe you just meant a text doc?)
Good luck!