I think understanding and generating are different things. I remember seeing an article days ago on this sub that says LLMs could translate languages they weren't trained on, so I'm not too surprised if you say it could translate Geringoso.

However it can't generate. When I tried to get it to write in Pig Latin, the sentences were incoherent and it contained words that aren't real words. But at least they all end with “ay” and the output was better than my initial approach.

My initial approach was to get ChatGPT to move the first letter of each word to the last (Pig Latin without the “ay”) to see if it's a viable way of avoiding the filter. And it completely failed. It ended up giving me sentences where every word is a typo like “Myh hubmurger js veyr dliecsoius” instead of “Ym amburgerh si eryv eliciousd”. On top of that, the filters could still detect the content with all those typos, so it was a failed experiment for me.