That mindset is a bit dated when models can pull up docs for a few years now. You can even have it write itself a little guide for lesser known languages within its own agents file.

The entire gleam language tour fits comfortably in a modern LLM context window. You're one web search away from "training" it yourself.

I'm not sure how much that matters. I suspect and anecdotally hear/see that compiler errors and docs are as/more important.

Programming models have been sophisticated enough for some time to not be restricted to specific languages. It's rather like the difference between a junior developer (who knows how to use a specific language) and a mid developer (who knows who to program generally).