Manual:Guide to setting up interwiki linking

Q: I'm puzzled about doing Interwiki links, the Interwiki.php is obsoleted... how do you set up interwiki links?

A: Before we can answer that, we must ask another question: do you need language links or just external interwiki links?

To set up new interwiki link prefixes, you stick them into the 'interwiki' table in the database (which is undocumented... the source code is the documentation).
 * Sample sql in the maintenance dir.
 * maintenance/interwiki.sql defines the standard prefixes
 * maintenance/wikipedia-interwiki.sql has the wikipedia language prefixes
 * set the magic global on then, and mark the local prefixes as local in the db
 * $wgInterwikiMagic = true; # Treat language links as magic connectors, not inline links
 * default is true
 * dirty secret: the 'local' field in the interwiki table is currently ignored. that's determined by whether the prefix is in the array of language codes/names defined in the language file