fallback language support for fonts (eg CJK priority)

Some Fedora users using CJK in English locales have requested desktop support for configuring secondary of fallback packages for text rendering (see posts: 1 and 2).

Firefox can handle this quite well. For GNOME users can set PANGO_LANGUAGE or FC_LANG, but it would be desireable to have some dconf setting to handle this which could then be exposed in gnome-control-center with gnome-settings-daemon?

What would be needed to make this happen?