> but LLMs can only learn languages that programmers write a sufficient amount of code in

i wrote my own language, LLMs have been able to work with it at a good level for over a year. I don't do anything special to enable that - just front load some key examples of the syntax before giving the task. I don't need to explain concepts like iteration.

Also llm's can work with languages with unconventional paradigms - kdb comes up fairly often in my world (array language but also written right to left).