Thank you for putting together SRFI 29.  It will be good to have a standard
way to do localization in Scheme.  I have just one suggestion:

Because it relies on FORMAT, SRFI 29 can't accomodate language ordering
variations.  In other words, it can't model the fact that one language may
require substitutions in a different order than another.  While Java code
for localization is often quite verbose, it handles this problem quite
nicely by using indexes in format strings, e.g.:

   http://java.sun.com/products/jdk/1.1/docs/api/java.text.MessageFormat.html

   Object[] arguments = {
       new Integer(7),
       new Date(System.currentTimeMillis()),
       "a disturbance in the Force"
   };
   String result = MessageFormat.format(
       "At {1,time} on {1,date}, there was {2} on planet {0,number,integer}.",
       arguments);
   : At 12:30 PM on Jul 3, 2053, there was a disturbance in the Force on
planet 7.

I would like to recommend changing SRFI 29 to support reordering in a
similar manner.