The YumLangpackPlugin Feature that I am planning to propose for F12
may help with this providing langpack-support metapackages.
https://fedoraproject.org/wiki/Features/YumLangpackPlugin
About the gdm menu itself I chatted to Ankit earlier in the week and came up with this
rfe:
https://bugzilla.redhat.com/show_bug.cgi?id=505484
asking if we could have some gdm system config to control which languages appear by
default in the menu.
Jens