"When an English speaker doesn't understand a word one says, it's "Greek to me". When a Hebrew speaker encounters this difficulty, it "sounds like Chinese". I've been told the Korean equivalent is "sounds like Hebrew"....And here's (some of) the information in the Wikipedia and Omniglot tables, presented as a directed graph courtesy of graphviz:" - Shannon Jiménez

Larger version of the graph at the link-- turns out Chinese is the most popular "incomprehensible" language. - Shannon Jiménez