Gracefully handle failure to install the current locale.

* guix/ui.scm (install-locale): New procedure.
* guix-build.in, guix-download.in, guix-gc.in, guix-import.in,
  guix-package.in: Use it instead of (setlocale LC_ALL "").

guix-build.in

@@ -220,7 +220,7 @@ Build the given PACKAGE-OR-DERIVATION and return their output paths.\n"))
                     name version)
              (leave (_ "~A: unknown package~%") name))))))
 
-  (setlocale LC_ALL "")
+  (install-locale)
   (textdomain "guix")
   (setvbuf (current-output-port) _IOLBF)
   (setvbuf (current-error-port) _IOLBF)

guix-download.in

@@ -134,7 +134,7 @@ and the hash of its contents.\n"))
                  (alist-cons 'argument arg result))
                %default-options))
 
-  (setlocale LC_ALL "")
+  (install-locale)
   (textdomain "guix")
   (setvbuf (current-output-port) _IOLBF)
   (setvbuf (current-error-port) _IOLBF)

guix-gc.in

@@ -155,7 +155,7 @@ interpreted."
                  (alist-cons 'argument arg result))
                %default-options))
 
-  (setlocale LC_ALL "")
+  (install-locale)
   (textdomain "guix")
   (setvbuf (current-output-port) _IOLBF)
   (setvbuf (current-error-port) _IOLBF)

guix-import.in

@@ -115,7 +115,7 @@ Import and convert the Nix expression ATTRIBUTE of NIXPKGS.\n"))
                  (alist-cons 'argument arg result))
                %default-options))
 
-  (setlocale LC_ALL "")
+  (install-locale)
   (textdomain "guix")
   (setvbuf (current-output-port) _IOLBF)
   (setvbuf (current-error-port) _IOLBF)

guix-package.in

@@ -598,7 +598,7 @@ Install, remove, or upgrade PACKAGES in a single transaction.\n"))
            #t))
         (_ #f))))
 
-  (setlocale LC_ALL "")
+  (install-locale)
   (textdomain "guix")
   (setvbuf (current-output-port) _IOLBF)
   (setvbuf (current-error-port) _IOLBF)

guix/ui.scm

@@ -26,6 +26,7 @@ (define-module (guix ui)
   #:use-module (ice-9 match)
   #:export (_
             N_
+            install-locale
             leave
             show-version-and-exit
             show-bug-report-information
@@ -45,6 +46,16 @@ (define %gettext-domain
 (define _ (cut gettext <> %gettext-domain))
 (define N_ (cut ngettext <> <> <> %gettext-domain))
 
+(define (install-locale)
+  "Install the current locale settings."
+  (catch 'system-error
+    (lambda _
+      (setlocale LC_ALL ""))
+    (lambda args
+      (format (current-error-port)
+              (_ "warning: failed to install locale: ~a~%")
+              (strerror (system-error-errno args))))))
+
 (define-syntax-rule (leave fmt args ...)
   "Format FMT and ARGS to the error port and exit."
   (begin