In the dev branch I've dumped the big array in Interwiki.php in favor of a table in the database; memcached is used to avoid hitting the database all the time.
I've also switched the order of checks in link parsing so that local namespaces are checked before interwikis. Among other things this should avoid the annoying problem we had briefly on Wiktionary where the 'Wiktionary' interwiki prefix was overriding the 'Wiktionary' namespace, making it impossible to link to such pages.
Further testing and tweaks on that part are likely useful.
Updated code running on http://test.wikipedia.org/
-- brion vibber (brion @ pobox.com)
wikitech-l@lists.wikimedia.org