system: Build system-wide locale definitions.

* gnu/system/locale.scm: New file.
* gnu-system.am (GNU_SYSTEM_MODULES): Add it.
* gnu/system.scm (<operating-system>)[locale]: Change the default to
  "en_US.utf8".
  (operating-system-locale-directory): New procecure.
  (operating-system-derivation): Use it.
* doc/guix.texi (Using the Configuration System): Change example locale
  to "fr_FR.utf8".
  (operating-system Reference): Add xref to "Locales".  Document
  'locale-definitions'.
  (Locales): New section.
* po/guix/POTFILES.in: Add gnu/system.scm.

gnu/system/locale.scm

@@ -0,0 +1,126 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2014 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu system locale)
+  #:use-module (guix gexp)
+  #:use-module (guix records)
+  #:use-module (gnu packages base)
+  #:use-module (gnu packages compression)
+  #:use-module (srfi srfi-26)
+  #:export (locale-definition
+            locale-definition?
+            locale-definition-name
+            locale-definition-source
+            locale-definition-charset
+
+            locale-directory
+
+            %default-locale-definitions))
+
+;;; Commentary:
+;;;
+;;; Locale definitions, and compilation thereof.
+;;;
+;;; Code:
+
+(define-record-type* <locale-definition> locale-definition
+  make-locale-definition
+  locale-definition?
+  (name    locale-definition-name)                ;string--e.g., "fr_FR.utf8"
+  (source  locale-definition-source)              ;string--e.g., "fr_FR"
+  (charset locale-definition-charset              ;string--e.g., "UTF-8"
+           (default "UTF-8")))
+
+(define* (localedef-command locale
+                            #:key (libc (canonical-package glibc)))
+  "Return a gexp that runs 'localdef' from LIBC to build LOCALE."
+  #~(begin
+      (format #t "building locale '~a'...~%"
+              #$(locale-definition-name locale))
+      (zero? (system* (string-append #$libc "/bin/localedef")
+                      "--no-archive" "--prefix" #$output
+                      "-i" #$(locale-definition-source locale)
+                      "-f" #$(locale-definition-charset locale)
+                      (string-append #$output "/"
+                                     #$(locale-definition-name locale))))))
+
+(define* (locale-directory locales
+                           #:key (libc (canonical-package glibc)))
+  "Return a directory containing all of LOCALES compiled."
+  (define build
+    #~(begin
+        (mkdir #$output)
+
+        ;; 'localedef' executes 'gzip' to access compressed locale sources.
+        (setenv "PATH" (string-append #$gzip "/bin"))
+
+        (exit
+         (and #$@(map (cut localedef-command <> #:libc libc)
+                      locales)))))
+
+  (gexp->derivation "locale" build
+                    #:local-build? #t))
+
+(define %default-locale-definitions
+  ;; Arbitrary set of locales that are built by default.  They are here mostly
+  ;; to facilitate first-time use to some people, while others may have to add
+  ;; a specific <locale-definition>.
+  (letrec-syntax ((utf8-locale (syntax-rules ()
+                                 ((_ name*)
+                                  (locale-definition
+                                   (name (string-append name* ".utf8"))
+                                   (source name*)
+                                   (charset "UTF-8")))))
+                  (utf8-locales (syntax-rules ()
+                                  ((_ name ...)
+                                   (list (utf8-locale name) ...)))))
+    (utf8-locales "ca_ES"
+                  "cs_CZ"
+                  "da_DK"
+                  "de_DE"
+                  "el_GR"
+                  "en_AU"
+                  "en_CA"
+                  "en_GB"
+                  "en_US"
+                  "es_AR"
+                  "es_CL"
+                  "es_ES"
+                  "es_MX"
+                  "fi_FI"
+                  "fr_BE"
+                  "fr_CA"
+                  "fr_CH"
+                  "fr_FR"
+                  "ga_IE"
+                  "it_IT"
+                  "ja_JP"
+                  "ko_KR"
+                  "nb_NO"
+                  "nl_NL"
+                  "pl_PL"
+                  "pt_PT"
+                  "ro_RO"
+                  "ru_RU"
+                  "sv_SE"
+                  "tr_TR"
+                  "uk_UA"
+                  "vi_VN"
+                  "zh_CN")))
+
+;;; locale.scm ends here