Or you can do "the inverse", by doing this:
1. *Do not* install fontconfig from Guix, but make sure to have fontcofig
installed in your foreign distro.
2. Make the file "$XDG_CONFIG_HOME/fontconfig/fonts.conf" with contents:
# Begin of file
<fontconfig>
<dir>~/.guix-profile/share/fonts</dir>
</fontconfig>
# End of file
3. Do:
$ fc-cache -rfv
So, the way I see it is that we have to tell the user that he must make
such "$XDG_CONFIG_HOME/fontconfig/fonts.conf" and choose whether he'll
be using the foreign distro's fontconfig or the fontconfig from Guix,
and chnage this "fonts.conf" file I just mentioned accordingly. If
people agree on, I can contribute with this documentation.
For those willing to explore the issue more: I read the user
documentation for Fontconfig, and it has a variable called
FONTCONFIG_PATH, but it doesn't accept multiple values separated by
colon, it only picks the first value and ignores the rest (I tested it
with `FONTCONFIG_PATH="/etc/fonts:$GUIX_PROFILE/etc/fonts" fc-cache
-rfv` and with `FONTCONFIG_PATH="$GUIX_PROFILE/etc/fonts:/etc/fonts"
fc-cache -rfv` and they resulted differently, but the only common point
was the fonts found inside "$XDG_DATA_HOME/fonts" because both places
referenced in FONTCONFIG_PATH paths have a "fonts.conf" file that has a
part similar to "<dir prefix="xdg">fonts</dir>").
