An older bug (https://issues.guix.info/issue/37662) discusses a similar
issue, but for a foreign distro with Guix installed (not a native Guix
distribution).

That bug mentions two things:

- make sure that either ‘glibc-utf8-locales’ or ‘glibc-locales’ is
installed (as root)
- make sure that the GUIX daemon is configured to use a UTF locale so it
can handle the UTF-encoded filenames in the nss-certs package.

I'm not sure whether these issues apply to a native Guix distribution. What
I do know is that when I encountered the error myself (running Guix on
Debian 10) I needed one additional thing: the environment of the user
installing the package had to include a UTF locale. After switching this
environment from LANG=C to LANG=en_US.utf8, the package installed without
issue.