The Babel Fish is well known from Douglas Adams, of course. It extracts meaning from sound waves and convert them into a psychic matrix which it excretes into your ear, thus giving you the ability to understand foreign languages.
But it only works on spoken language, doesn't it. The written word is a mystery to the Babel Fish.
But as long as the foreign language is in Latin Script, you'd be all right, I reckon. Even if you don't understand the language, you could just read out the writing. Then the Fish will hear the words, and translate- as best it can- into your native language. Of course, it would only translate as well as you were able to read the foreign language. I reckon for most things I'd try to read, all languages would sound like Swedish.