Tossed this together during hacking this evening in Berlin, finally fixes https://bugzilla.wikimedia.org/show_bug.cgi?id=14473
Somehow we never got round to recording interwiki links into the database link tables (eventually langlinks was added, but only for the sidebar interlanguage links; inline interwiki links were simply dropped).
The table will be added by update.php for MySQL, should work for SQLite (untested); probably still need to add a PostgreSQL updater for it.
Note that the magic indirection for things like [[wikt:fr:blah]] isn't resolved on the source wiki side, so that'll currently record as ('wikt', 'fr:blah'). At some point we'll probably want to make the project/language pairings something we can evaluate and normalize to provide better tracking.
-- brion vibber (brion @ pobox.com)