There is a wee typo in the systemd file *guix-daemon.service* installed on
Ubuntu 20.04 by the guix-install.sh script.
The text of */root/.config/guix/current/lib/systemd/system/guix-daemon.service
*contains the text:

Environment='GUIX_LOCPATH=/var/guix/profiles/per-user/root/guix-profile/lib/locale'
LC_ALL=en_US.utf8

The portion .../guix-profile/... should read .../*.guix-profile/*..., in
other words the path as given omits the requisite single period (.) as the
prefix of the directory .guix-profile.

This minor oversight accounts in part for the  *guile: warning: failed to
install locale *error and related warnings that have cropped up repeatedly
when the build daemons are invoked

To test this fix:

   - I edited the guix-daemon.service specification in place at
   /etc/systemd/system by hand
   - Rebooted to restart the guix build daemons (I detest systemd and I'm
   lazy besides)
   - *guix pull *for my personal userland account
   - *guix package -u* to upgrade same
   - *guix package -i libc-utf8-locales* to upgrade my locales from 2.29 to
   2.31
   - *sudo -i guix pull* to update the root's view of guix
   - *sudo -i guix package -u* for an upgrade of same
   - *sudo -i guix package -i glibc-utf8-locales* to have the latest
   version of the UTF-8 locales installed in ~root/.guix-profile/lib/locale

In subsequent user-level *guix install X* commands the warning no longer
appears nor do the build daemons complain about failing to set the locale
to *en_US.utf8*