installer: Sort keyboard layouts according to language and translations.

Previously, we would always (1) put English first, and (2) sort the
other layouts based on their English description.  This fixes both
issues.

* gnu/installer/newt/keymap.scm (sort-layouts)[layout<?]: New procedure.
[preferred]: New variable.
Partition according to both the 'name' and 'synopsis' fields.  Sort both
the main layouts and the other layouts according to 'layout<?'.

gnu/installer/newt/keymap.scm

@@ -28,6 +28,7 @@
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
+  #:use-module (ice-9 i18n)
   #:use-module (ice-9 match)
   #:export (run-keymap-page
             keyboard-layout->configuration))
@@ -64,14 +65,29 @@
 
 (define (sort-layouts layouts)
   "Sort LAYOUTS list by putting the US layout ahead and return it."
+  (define (layout<? layout1 layout2)
+    (let ((text1 (x11-keymap-layout-description layout1))
+          (text2 (x11-keymap-layout-description layout2)))
+      ;; XXX: We're calling 'gettext' more than once per item.
+      (string-locale<? (gettext text1 "xkeyboard-config")
+                       (gettext text2 "xkeyboard-config"))))
+
+  (define preferred
+    ;; Two-letter language tag for the preferred keyboard layout.
+    (or (getenv "LANGUAGE") "us"))
+
   (call-with-values
       (lambda ()
         (partition
          (lambda (layout)
-           (let ((name (x11-keymap-layout-name layout)))
-             (string=? name "us")))
+           ;; The 'synopsis' field is usually a language code (e.g., "en")
+           ;; while the 'name' field is a country code (e.g., "us").
+           (or (string=? (x11-keymap-layout-name layout) preferred)
+               (string=? (x11-keymap-layout-synopsis layout) preferred)))
          layouts))
-    (cut append <> <>)))
+    (lambda (main others)
+      (append (sort main layout<?)
+              (sort others layout<?)))))
 
 (define (sort-variants variants)
   "Sort VARIANTS list by putting the international variant ahead and return it."