While the URL http://www.gentoo.org/doc/en/handbook/ correctly shows the english handbook index, the URL http://www.gentoo.org/doc/fr/handbook/ is redirected on http://www.gentoo.org/doc/en/fr/handbook/index.xml which doesn't exist. Note that this apply for other languages too.
Create (translate) an index file :) http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/handbook/index.xml?cvsroot=gentoo&sortby=date
Aaaah right, we just missed this one ;o) Sorry for noise