[Fontconfig] Localized family and style names for user interfaces

[Keith Packard]

TrueType fonts have this nice feature -- they may include multiple family 
and style names, each with a language tag (not RFC 3066 based, but 
we can't have everything).  It would be nice if fontconfig-based 
applications could display and accept these names as appropriate.

Converting the TrueType language information into RFC 3066-based language 
tags should be relatively straightforward.  In cases where there isn't a 
1<->1 mapping, we can use multiple RFC 3066 tags as needed.  The existing 
string values can be augmented in some way to tag each one.  Building a 
reasonable API to get at the language tags may be a bit harder.

One of the fontconfig design principles is the separation between font
matching and font listing.  Information presented to the user about
available fonts is expected to come from the font listing functions, not
the font matching functions.  So, it seems reasonable to expect that 
providing some mechanism to adjust what values are returned from the 
listing functions should be sufficient to localize displayed font names.

I suggest that a new API (FcFontListLang?) be created which accepts a list 
of language tags and sorts all of the strings based on that list.  The 
existing FcFontList API would convert the current locale to a language tag 
and call this new function.

At first blush, the font matching API needs no changes; fonts would simply 
have multiple family/style values and match any of them.  I'd like to try 
this simplistic approach at first, but I'm a bit afraid that collisions 
between names in different languages will necessitate a more complex 
solution.   I guess we'll see what happens.

Does any of this seem horribly wrong?

-keith