For those curious about the idiom, "It's Chinese to me," here's the directed graph of prevailing "It's X to me" idioms among world languages:
It makes sense, too- Considering a given language, another language that is much newer wouldn't have existed when the phrase was created, and a language of the same age or only a little newer, was probably not widespread enough to be referenced when the phrase was coined.
http://www.omniglot.com/language/idioms/incomprehensible.php
^ Worth noting that 'chinpunkanpun' is the word; the rest of the phrase is accurate Japanese.
Except of course for the phrase "it's your mom to me"