I find that most people who don't use terminals don't do it out of pure preference for GUIs over CLIs. Instead, they use GUIs because they simply don't want to spend time learning how to use CLIs.
If they did, I bet 90% of people would move over.
It both is and isn't "a whole language". Most commands just execute a single program with options and/or arguments, except you don't have the overhead of opening a GUI, finding the right dropdown menu, etc. You quickly start to pick it up like you would a spoken language, remembering the "words" for actions, and it becomes a very natural way to think.
IMO the biggest stumbling block is just learning how to type efficiently. This includes knowing about tab completion, history search, putting stuff in your .bashrc and so on.