Cyberdog Idea: Formalized XML for translated documents. One file contains two or more translations of the same document. Each corresponding paragraph, line, etc of the document in each translation is marked up with the same identifiers. That way, if you're reading a document in a language you're learning and you're stumped on a line or word, you could see the same line or word translated into a language you already know, among other applications.

Adam Douglas ASP.NET's XML-based Local Resource Files fulfill this role. Of course you then have to work with ASP.NET but just saying.