A multi lingual site using YACS

You know those sites where by cliking on a flag or language icon you can  choose to see the content of the site in e.g. English, French or German.

How would one do that with YACS.

For a small project I'm working on I must be able to have the content in Dutch and French with changing using a simple click.

If possible the default language shown should depend on the browser settings.