How about adding a configuration page to manage languages from administration backend, like in Joomfish (Joomla translation component) http://img23.imageshack.us/img23/8430/joomfish.png ? Name, short code, active, default and order columns would be necessary. That way we could have a language switching component in frontend which could list all active languages and their names. Also adding new translations could be simplified - no more manual creation of pages with _lang-code suffix.
Another important thing would be display of menu items only if they have translations in that language.
Another important thing would be display of menu items only if they have translations in that language.