If this does appear to become a problem, is it not hard to apply the same RLHF infrastructure that's used to get LLMs effective at writing syntactically-correct code that accomplishes sets of goals in existing programming languages to new ones.
That would make sense if LLMs understood the domains and the concepts. They don't. They need a lot of training data to "map" the "knowledge transfer".
Personal anecdote: Claude stopped writing Java-like Elixir only some time around summer this year (Elixir is 13 years old), and is still incapable of writing "modern HEEX" which changed some of the templaring syntax in Phoenix almost two years ago.