I've always looked at not only languages, but libraries and APIs, as user-interfaces. It's not just about what it lets you do, it's about how much sense it make

I've always looked at not only languages, but libraries and APIs, as user-interfaces. It's not just about what it lets you do, it's about how much sense it makes. Interfaces should be shaped to guide the user into proper usage, to adhere to assumptions the user will make about the underlying behavior, and to leverage things like Gestalt principles to draw connections between different facets.