That's not quite true in my experience; AI can pick up new languages very quickly and are able to adapt to novel syntax and semantics with just a description and a few examples. What's also baked into the AI are decades of PL research and it can quickly deploy esoteric PL concepts not found in 99% of languages.

In my experience it's rather people who have the most trouble with new languages, as the difference between the PL frontier and languages that most people use is quite extreme.

Conversely, AI is adept at staking out a point in the PL design space and developing a grammar and vocabulary around it. Then it writes a parser and interpreter to execute whatever semantics, writes a standard library to support writing programs, and finally writes the compiler in itself.

Because it's so good at doing this you can do a lot of exploration whereas before it would take years now it takes months.