My suggestion for handling the index page is as follows:
if there is no value in index_page parameter:
- Check for the locale (default_language) and return the appropriate xx:index page, where xx is the lang
- If there is no xx:index page for this locale, fall back to system_locale::index
if there is a value in index_page parameter:
- If the value is like xx:mypage, then return the xx:mypage, meaning in the locale which is given by "xx"
- If the value is "mypage", then return mypage in the locale of whatever default_language returns, or fall back to the system_locale version of the page.
