Set "GUIX_LOCPATH" in 'guix-daemon.service'.

Suggested by Thomas Danckaert <thomas.danckaert@gmail.com>.

* etc/guix-daemon.service.in (Environment): New value.

etc/guix-daemon.service.in

@@ -7,6 +7,7 @@ Description=Build daemon for GNU Guix
 
 [Service]
 ExecStart=@bindir@/guix-daemon --build-users-group=guixbuild
+Environment=GUIX_LOCPATH=/root/.guix-profile/lib/locale
 RemainAfterExit=yes
 StandardOutput=syslog
 StandardError=syslog