Reference from: Google mail list thread.
It has been decided that 1.6 would not be fully multilingual, i.e. it would not be a replacement for Joomfish where each item has its equivalent. Was also decided to have a language Switcher (specially to use on frontpage) to display the items tagged for a specific language (Articles, categories, modules, ..)
The Switcher would, if also present on other pages than the Home, redirect to the home page and display these items.
Joomla 1.7 is introducing the possibility to associate menu items in different languages, thus redirecting via the switcher to the associated menu item, if parametered this way.
To get this, language fields have been created in the db and an interface in the UI where the items can be tagged. The Language Manager has 2 parts (Tabs):
This "Content" part, if used, lets designate a language (even if it is not yet installed) to populate the lists proposed for all Language fields tagging in the UI. The idea is that,
This lets user prepare a complete set of items assigned to a specific language without even installing that language. Then release it when ready. A non-registered user should get a cookie and a registered user should get its user's language params changed on the fly.
Tutorial is available here: Language Switcher Tutorial