Wouldn't an LLM just write a python script to convert an intermediate language without the triggering phrases and letter counting.

Yeah this is what they end up doing. The language itself isn't that hard for them, it's separating the language from the traps in the spec. I also tried making a hostile esolang, without all the prompt injections and whatnot, and it was very easy for LLMs. (It was mainly based around tokenizer quirks, like the r in strawberry test, but becomes trivial with scripts).

This depends on them being able to interpret the spec correctly. They could certainly write a Python script, but their implementation would need to match the spec. I haven't seen any model attempt it this way so far.

An LLM could equally decompile the binary, clean up the code, and recode it in one /goal.