Hi Guix!

This patch lets us localize package synopsis and description in package
lists. This is not super useful, because our guix-packages domain is
almost untranslated, for every language, but I think it's better than
nothing.

Locally, you can simply copy an existing guix-packages.mo (on the Guix
System,
/run/current-system/profile/share/locale/de/LC_MESSAGES/guix-packages.mo
for the German translation) to the local locale directory
(de/LC_MESSAGES/guix-packages.mo), in the same way we do for the
guix-website domain.

I also modified .guix.scm so the website can be generated with
localized packages. I used the latest guix package from the current
guix, because latest-guix (defined in .guix.scm) does not have any
locale information in it (mo or po). Any idea to get the latest
translations instead?