user-record: Add languages field

This field is like preferredLanguage, but takes a priority list of
languages instead. If an app isn't translated into a user's primary
language, it can fall back to one of the other languages in the list
thus making the app more accessible to the user.

For instance: in my experience, many Ukrainians are fluent in Russian,
often significantly better than English (especially if they are of a
generation that grew up during the USSR). Such a person might set this
new variable to ["uk_UA.UTF-8", "ru_UA.UTF-8"] so that software that
lacks Ukrainian translations will first try Russian translations before
defaulting to English.

Fixes #31290

shell-completion/bash/homectl

@@ -146,6 +146,9 @@ _homectl() {
             --cifs-user-name)
                 comps=$(compgen -A user -- "$cur" )
                 ;;
+            --language)
+                comps=$(localectl list-locales 2>/dev/null)
+                ;;
         esac
         COMPREPLY=( $(compgen -W '$comps' -- "$cur") )
         return 0