bug#12008: Alphabetic sorting respect user's language and/or locale

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 21 Jul 2012 16:32:50 +0200
> From: martin rudalics <rudalics@gmx.at>
> 
> Currently, specifying alphabetic order for output produced by functions
> like `dired' and `sort-subr' makes that output appear in ASCII-code
> order.  This means that such output deviates from the order expected by
> users of Latin-derived alphabets like French, German or Spanish and
> can make working with these functions very awkward.
> 
> Please consider adding a predicate which makes it possible to produce
> such output in alphabetic order respecting the language and/or locale
> of the user.

A simple way of doing this goes along the following lines:

  Lisp_Object enc_str1 = ENCODE_SYSTEM (string1);
  Lisp_Object enc_str2 = ENCODE_SYSTEM (string2);

  return make_number (strcoll (enc_str1, enc_str2));

However, there are 2 potential issues with this:

 . do typical libc implementations of strcoll handle multibyte
   characters correctly, if ENCODE_SYSTEM happens to produce multibyte
   encoding, such as UTF-8?

 . is the above efficient enough, when ENCODE_SYSTEM is not a no-op
   (which it is for UTF-8 locales)?

I don't know the answer to these, mainly to the first.  (The
MS-Windows implementation is claimed to handle multibyte strings.)
Anyone?