Allegedly, "The Japanese use a string of nonsense syllables which imitate the sounds of unknown languages, especially Chinese"

http://www.omniglot.com/language/idioms/incomprehensible.php

^ Worth noting that 'chinpunkanpun' is the word; the rest of the phrase is accurate Japanese.

I thought about that for a whole when that post first came up, but came to the conclusion that there really isn't one. English would be the closest example of what people say they can't speak, but there's no "it's xx to me" that I'm aware of...

Except of course for the phrase "it's your mom to me"