I think "typo3" has this feature. basically it checks the user's browser language setting and will display the site in that language if available. if the language is not available the default language will be used. the user can at any time choose whichever langue he/she wants and store this setting in his/her preferences.
this would be a nice feature for sites needing to publish in more than one language.
of course it would also be nice to have some kind of workflow gui for this in the admin interface, e.g. author X posts article in english, queues it for publishing and tags "french" and "german" as "required translations before publishing". the editors for that language then will find that article in their queue, can translate it and tick it off for publishing. once all publishing requirements are met the article goes up front.