In Chinese we say it's "book from heaven"("天书"), for incomprehensible writings. That's the end of the this English...->Geek->Chinese->heaven sequence
For speakings, yes it's "bird language" ("鸟语"), but the "bird" here is used as a euphemism for male genital.
BTW Chinese is an analytic language, so the grammar is actually very easy.
> In mythology, medieval literature and occultism, the language of the birds is postulated as a mystical, perfect divine language, green language, Adamic language, Enochian, angelic language or a mythical or magical language used by birds to communicate with the initiated.
I read that article a while ago, and until a moment ago assumed this discussion was about it. "Atlas Obscura" and "Strange Maps" are similar enough that I got them mixed up.
EDIT: Looks like Hebrew speakers use Chinese, so we're in a loop.
Spoiler alert: it’s Chinese.
Interestingly enough, I took the family to Greece just last month and explained to the children that in English, it is said that something sounds Greek if it cannot be understood. My oldest was wise enough to ask why, if Greek is the root of so many English words. I still don't have an answer for her!
Those schools also taught Ancient Greek for advanced students to be able to read philosophy and portions of the Bible. This was useful if you wanted to be a priest, but otherwise it was just a pointlessly hard course for most students.
Additional "fun" fact: in modern Greek, the onomatopoeia for "babbling" is "burbur".
Based on the linked scale it is more accurate to say Japanese instead.
That's because we are still studying Greek and Latin on some public school.
If you don't understand, you would say "Mi sembra arabo" (it seems arabic to me) but if you are talking and the other part doesn't understand it is more common "E che parlo, turco?" (what am I speaking, turkish?) than "E che parlo, arabo?" (what am I speaking, arabic?) at least in my experience.
Of course historically "turk" and "arab" were synonyms due to the fall of of Constantinople and the "contacts" with the Ottoman Empire.
And now, risking to quote myself, evidence of the sentence (by a greek) "it's English to me":
A more "neutral" Italian would be "Parlo forse turco?".
Curiously, it is a sentence used in literature by Andrea Camilleri which should mean that the form is also in use in Sicily.
JFYI ;-) Mario Vigorone :
BTW, I agree with the other comment that this is more common in the north.
A minority today, but one would assume (as in the case in e.g. German and France) more (of students) in the past 50-100-200 years when the phrase was established.
When someone makes mistakes in English we say they speak English like a Spanish cow.
As for learning Japanese, believe me, it's nothing compared to Greek -- there are not as many tenses, nor genders, nor verb conjugations I'd suggest it's very similar to Hebrew which itself is rather similar to Greek in many ways
Another expression relating to a confusing mess is the wonderful Hungarian Flood-resistant mirror-drilling machine:
"Before Unicode became common in e-mail clients, e-mails containing Hungarian text often had the letters ő and ű corrupted, sometimes to the point of unrecognizability. It is common to respond to an e-mail rendered unreadable (see examples below) by character mangling (referred to as "betűszemét", meaning "garbage lettering") with the phrase "Árvíztűrő tükörfúrógép", a nonsense phrase (literally "Flood-resistant mirror-drilling machine") containing all accented characters used in Hungarian."
 Australia here. What in the U.S. is apparently called take-out is called take-away here.
Greeks use Chinese as the canonical example of an incomprehensible language.
What's interesting is that although the "It's Greek to me" colloquialism mostly refers to the fact that the Greek alphabet seems incomprehensible to the (non-classical-humanities-educated) reader, Greek has actually a very complex grammar: Everything is conjugated, everything has genders, and you have to remember the correct form of every noun, preposition, article, pronoun, etc. In comparison, Chinese grammars are amazingly simple.
Most Greeks don't take notice of this fact until they see somebody struggling to learn Greek as a foreign language.
Not to mention the fact that ancient Greek seems like a foreign language to modern Greek speakers. Interestingly ancient Greek is more compact and comprehensive (ie uses fewer words compared to modern) as it uses a richer grammar (tenses, voices, etc)
It's not as difficult as you'd expect, because word genders are derived from the suffix, with very few exceptions (e.g. η ψήφος). Compare with German, where there's no relation between the word and the gender (you just have to memorize all of them) and they still have the dative. This makes German grammar a superset (and strictly more complex) than Greek grammar.
As in: Am I talking Chinese to you?
And: That seems Spanish to me. Meaning"that doesn't seems to be right.
And if I am not able to grasp something I would say: I only understand train station.
For the train station, we don't have something that means the same that I can think of right now, but a similar one is "my name is Haas". You can say it when you suspect someone just pretends not to know anything about it, but about yourself it can be used either way. Seems to be a purely Dutch thing, I looked up the Wikipedia and discovered that it does not have anything to do with the animal "haas" (hare). Somewhat unsurprisingly, it comes from a story about a German:
Paraphrased in English: The saying probably stems from an event in 1855, where a German student wanted to flee to France. To cross the border, he needed an identity card, which he got from a classmate, Victor von Hase. Von Hase then claimed he lost his ID, but it was later found in France, where the murderer had lost it. The real Von Hase had to appear in court and that is where he spoke the words millions would come to speak after him: "Mein Name ist Hase [...] ich weiß von nichts." (My name is "hare", I don't know anything about this.)
I’d put that down to the notoriety requirements of the German Wikipedia which are somewhat peculiar.
Edit: It’s mentioned on this Wikipedia page https://de.m.wikipedia.org/wiki/Victor_Hase and TIL: The expression was coined in the city I was born in.
The literal translation is therefore "I don't understand hölkäsen pöläys" :P
As for Japanese being harder than Mandarin and Cantonese, I think it's true if one considers complete mastery of the language but I would say that Japanese is easier to master orally for day to day life than either Mandarin or Cantonese.
But I only ever heard this one in Saxony, which borders the Czech Republic.
Interesting that so many comments here talk about spanish being used as equivalent for "greek" in their culture.
We would say that something was "Double Dutch", not that it was "Greek to me".
Which seems to suggest that "Double Dutch" (and "High Dutch") actually refer to the German language.