It's All Greek To Me
If I only had a dollar (inflation from a dime) for every time I have heard this.
As a Greek teacher I often hear this idiom which is a literary way of saying "I don't get it." Although Greek may be most often referenced as the icon for unintelligible communication, Chinese appears to be not too far behind. Take a look at Wikipedia's list of similar phrases between other languages. Since neighboring communities often poke fun at each other through all sorts of jokes it isn't surprising to see this type of idiom develop between so many languages. I believe Greek is so widely known for a number of historical reasons. Greek has played a part in western literature through the New Testament and Greek classics. Historically, the language of this litterature was an obstacle and had to be translated. The Greek were also displaced by the Turks which sparked a revival in Greek literature and later the Renaissance. This brought Greek with its foreign looking alphabet into the western cultural spotlight. Then the idiom was indelibly inscribed into western history through Shakespeare's use of it. Now it is so commonly known that whenever the topic of Greek comes up someone cannot help but demonstrate that they are still holding this thread of history.
In Julius Caesar (1599), William Shakespeare made this idiom forever famous to all English speakers. However, it should be noted that the quote works on two levels in the play since the character (Casca) who speaks the line had just returned from hearing Cicero speak Greek. Here is the quote "Those that understood him smiled at one another and shook their heads; but for mine own par, it was Greek to me."
Thomas Dekker was an Elizabethan playwright contemporary with Shakespeare. He used the phrase in one of his plays just prior to Shakespeare's Julius Caesar. However, he uses a rather odd phrasing of the line since it nearly always used in the first person (with any language) rather than the third. Here is the quote "I'll be sworn he knows not so much as one character of the tongue. Why, then it's Greek to him."
Medieval Latin Proverb
As you have notice that his idiom is merely an English-Greek phenomenon it shouldn't be surprising to learn that it has older roots in Medieval Latin. "Graecum est; non potest legi" (It is Greek; it cannot be read) St. Augustine would have agreed and probably uttered that Latin idiom.