Yes, it's true that someone can put together a simple language like in a university course. The difficulties, as mentioned at the bottom of the post, are things like metaprogramming features or optimizing compilers.
The tail ends of a language implementation (parsing and code generation) are a fixed cost; the "middle end" can grow unbounded as more production-quality items are added.
The tail ends of a language implementation (parsing and code generation) are a fixed cost; the "middle end" can grow unbounded as more production-quality items are added.
My language: https://www.empirical-soft.com