diff --git a/guix/scripts/substitute.scm b/guix/scripts/substitute.scm
index e0a694ad0f6404e4c4f4756c0f67a89e0dd809f8..fa1dd09df8a6d607cbaf2c4bbd7196afde741c68 100755
--- a/guix/scripts/substitute.scm
+++ b/guix/scripts/substitute.scm
@@ -1000,6 +1000,13 @@ (define (guix-substitute . args)
   (newline)
   (force-output (current-output-port))
 
+  ;; Attempt to install the client's locale, mostly so that messages are
+  ;; suitably translated.
+  (match (or (find-daemon-option "untrusted-locale")
+             (find-daemon-option "locale"))
+    (#f     #f)
+    (locale (false-if-exception (setlocale LC_ALL locale))))
+
   (with-networking
    (with-error-handling                           ; for signature errors
      (match args
diff --git a/guix/store.scm b/guix/store.scm
index af311a0ebdfd9c67b4538dc090e006bf4fbada94..8d1099dab20c31da792dd84e70cfa0e40b9d0d30 100644
--- a/guix/store.scm
+++ b/guix/store.scm
@@ -534,7 +534,10 @@ (define* (set-build-options server
                             (substitute-urls #f)
 
                             ;; Number of columns in the client's terminal.
-                            (terminal-columns (terminal-columns)))
+                            (terminal-columns (terminal-columns))
+
+                            ;; Locale of the client.
+                            (locale (false-if-exception (setlocale LC_ALL))))
   ;; Must be called after `open-connection'.
 
   (define socket
@@ -573,6 +576,9 @@ (define socket
                      ,@(if terminal-columns
                            `(("terminal-columns"
                               . ,(number->string terminal-columns)))
+                           '())
+                     ,@(if locale
+                           `(("locale" . ,locale))
                            '()))))
         (send (string-pairs pairs))))
     (let loop ((done? (process-stderr server)))