I recently used this phrase in a picture book draft on Day 5 of NaPiBoWriWee. The number five inspired my foray into non-fiction: a picture book exploring the Pentagon, (from the Greek pentagōnon). The word is a metonym, used like Washington is when the U.S. government is implied, or Hollywood for the film industry (also used to diss cookie-cutter happy endings).
Back to the Greek (which metonym stems from): a somewhat Ionic (or Corinthian) reply when something incomprehensible had been uttered instead of the more Doric “Huh?” or “Wha?” So who said it first? I’ll put my money on a Latin-speaking Roman on his high horse saying, “Graecum est; non legitur” (“it is Greek, [therefore] it cannot be read”).
On my first search attempt I found this GREAT site: Omniglot: the online encyclopedia of writing systems and languages. Where you can find translations from Arabic to Yiddish. It seems most cultures hear some other language when spoken as gibberish, but I need to award a gold-star-sticker to the silliest sounding translation from the Cebuano-speaking people of the Philippines, referring to Chinese: Ching chong ching chang ching! (Got that one from Wikipedia!)