There's no final answer to the question "which language should I learn?" but I'll offer you my two cents anyway. If development speed is of the essence, you may be better off trying a scripting language rather than C. I heard good things about Lua, but use Python for my own project, and have been happy with that. It has stuff like memory handling built-in, so you can pretty much get straight to business. On the down side, Python is not good at heavy lifting, but it's sufficient for a typical, turn-based Roguelike. If graphics rendering becomes a bottleneck, it's usually because the programmer is doing something wrong. Bits of code I have had to optimize include world generation (although a few seconds of load time when the game starts isn't a huge catastrophe) and AI routines (when you have hundreds of actors looping over detailed calculations). For graphics rendering and other handy tools, it's worth checking out
Pygame or
libtcod (which is tailored to Roguelikes in particular).
Another option for you might be to consider using a full-fledged game engine. The most popular one is arguably Unity, although I like
Godot myself. It's open source, in active development, and uses a scripting language quite similar to Python. I only tried it briefly, but it was quick to pick up (I had a playable framework for a Pooyan clone after a few hours), and it seemed versatile enough for a variety of projects.
As always,
Minotauros