reset to default locale

We have found that some things like Grub inherit the environment
during the upgrade process, which turned its interface in french on
nutans.

tsa/howto/upgrades/buster.mdwn

@@ -5,9 +5,10 @@ Procedure
 
  1. Pre-upgrade backups and preperation:
 
-        # note: that screen call does not really work this way
-
+        : reset to the default locale
+        export LANG=C.UTF-8
         sudo apt install ttyrec screen debconf-utils apt-show-versions deborphan &&
+        # note: that screen call does not really work this way
         sudo ttyrec -e screen /var/log/upgrade-buster.ttyrec &&
         ( umask 0077 &&
           tar cfz /var/backups/pre-buster-backup.tgz /etc /var/lib/dpkg /var/lib/apt/extended_states /var/cache/debconf &&