Babelfish--even poissoble?

Has anyone seen, read, heard of The Hitchhiker's Guide to the Galaxy? There's a character that helps to decode the languages of non-English speaking aliens, called the "Babelfish." It's a sort of instant translator that works by receiving the electric brainwaves from the mind of the speaker and translating them into English. No problem, right? Sounds great! But...would it work? Thinking about Saussure, Sapir, Barthes, Austin, and even Foucault, at how we use language to understand each other. What episteme do martians who hyper-warped into our universe from year 5872 belong to?