Wikibooks is internally multi-lingual so there is no
need for sub-domains. The
foundation owns and controls
wikisource.org and I no longer have access to it
to change settings. That project is *also* internally multi-lingual and thus
there is no need for subdomains (they would also be very repetitive since the
same source docs will need to be used in many different languages).
What we need is the ability to switch user interface language in the same wiki.