Why do we say "It's all Greek to me"?

Meaning:

It's unintelligible.

Background:

Some sources say that this expression originates from the notations of Medieval scribes copying Latin text who, if faced with a quote in Greek (or maybe other languages) they could not translate, would write Graecum est, non legitur or Graecum est, non potest legi—It is Greek; it cannot be read.

Although Shakespeare did not coin "it's all Greek to me" (as it's found in an English translation of an Italian play decades earlier), we owe its popularity to his 1599 play, The Tragedy of Julius Caesar:

Cassius: Did Cicero say any thing?

Casca: Ay, he spoke Greek.

Cassius: To what effect?

Casca: Nay, an I tell you that, I'll ne'er look you i' the face again: but those that understood him smiled at one another and shook their heads; but, for mine own part, it was Greek to me. I could tell you more news too: Marullus and Flavius, for pulling scarfs off Caesar's images, are put to silence. Fare you well. There was more foolery yet, if I could remember it.

If English speakers say "it's all Greek to me," what do they say in Greece and other countries?

According to Wikipedia, the Norwegians and Swedes join us English speakers in thinking it's all Greek to them; the Czechs think it's all Spanish; the Bulgarians think it's Patagonian; the Indonesians think it's chicken feet (i.e. gibberish); and the Greeks will shrug and, apparently, say "this strikes me as Chinese," - a view shared by Russians and a good chunk of Eastern Europeans.

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