I don't know if it would be interesting and possible to have an extension with which you can make your website multilangual either in combination with a database or XML files.
I know the easy way is to just create a mirror folders of your site in the different languages and direct users to the right mirror folder of their language. However it would be more interesting if you can store different keylines of text or whole topics in different languages in a table or xml file and show the right language of that on the same page depending on the language of the user. That way it will be easy to update the tables or files with other languages by yourself or even by other users.
I never saw an extension that can help doing this so maybe it's an idea. If more people like this idea then share this and maybe it will come someday.