Yesterday I was able to do something similar. I bounced back and forth with the AI to design a programming language and asked the AI to write code in that language. Here is the conversation transcript. And here is an explanation of the language and what it is used for.

I think the most impressive thing is that the AI was able to write correct code (most of the time) in this new language despite the new language having a significantly different structure from other programming languages. Converting code from other languages to this new language is non-trivial, but the AI was able to do it.

It has to, to some extent, understand what is happening in the code when the same problem is solved in other languages, and then be able to apply that logic to the new language.