Nah. People have been translating the Ancient Greek classics into English since English became a respectable language five or six hundred years ago. I think the difficulty of translation correlates with the difference in the world views of the two language communities. To be sure, Ancient Greece was an Iron Age civilization and we're two Paradigm Shifts ahead of them in the Post-Industrial Era, so some of the things that were important to them are inconsequential to us--or even incomprehensible. Still, I think it would be harder to translate Modern English into Ancient Greek than vice versa. And of course the real issue is that Ancient Greek isn't really a dead language. University classes in Greece are taught in the ancient language and the students read Plato's and Aristotle's original writings. The modern language has not diverged all that much from the ancient, it just has some new vocabulary. It's like us trying to read Shakespeare in Early Modern English, not Chaucer in Middle English or Beowulf in Anglo-Saxon. I think the greatest difficulty would come from two languages that represent entirely different perspectives on the universe. I'm thinking of Hopi: they don't even regard time the same way we do.
There are some translations which are simply impossible. I refer to the Piraha people of the Amazon. It's certainly possible to learn their language and get by day to day, but not everything in our culture can be translated into theirs. http://edge.org/3rd_culture/everett07/everett07_index.html
