Keith has this idea of for performance reasons rebuilding FcFontSort results
from FcFontMatch followed by a generic fallback list.  This doesn't work for
various cases, including for ":lang=en,ja" for example.

To be able to do something like that we need a new API that returns a list of
fonts explicitly chosen to fulfill the requested pattern (including stuff added
by the config file.)  That list then can be expanded by a generic fallback list
by the application.   Not sure how easy is to implement this.

Example:

[behdad@home ~]$ fc-match --sort | head -n 5
DejaVuLGCSans.ttf: "DejaVu LGC Sans" "Book"
DejaVuLGCSans.ttf: "DejaVu LGC Sans" "Book"
DejaVuLGCSans-ExtraLight.ttf: "DejaVu LGC Sans" "ExtraLight"
DejaVuLGCSans-BoldOblique.ttf: "DejaVu LGC Sans" "Bold Oblique"
n019003l.pfb: "Nimbus Sans L" "Regular"

[behdad@home ~]$ fc-match --sort :lang=fa | head -n 5
roya.ttf: "Roya" "Regular"
DejaVuLGCSans.ttf: "DejaVu LGC Sans" "Book"
DejaVuLGCSans.ttf: "DejaVu LGC Sans" "Book"
DejaVuLGCSans-ExtraLight.ttf: "DejaVu LGC Sans" "ExtraLight"
DejaVuLGCSans-BoldOblique.ttf: "DejaVu LGC Sans" "Bold Oblique"

[behdad@home ~]$ fc-match --sort :lang=fa,ja | head -n 5
roya.ttf: "Roya" "Regular"
sazanami-gothic.ttf: "Sazanami Gothic" "Gothic-Regular"
DejaVuLGCSans.ttf: "DejaVu LGC Sans" "Book"
DejaVuLGCSans.ttf: "DejaVu LGC Sans" "Book"
DejaVuLGCSans-ExtraLight.ttf: "DejaVu LGC Sans" "ExtraLight"

[behdad@home ~]$ fc-match --sort Nazli:lang=fa,ja  | head -n 5
nazli.ttf: "Nazli" "Regular"
sazanami-gothic.ttf: "Sazanami Gothic" "Gothic-Regular"
DejaVuLGCSans.ttf: "DejaVu LGC Sans" "Book"
DejaVuLGCSans.ttf: "DejaVu LGC Sans" "Book"
DejaVuLGCSans-ExtraLight.ttf: "DejaVu LGC Sans" "ExtraLight"