Wikimedia Bugzilla is closed!

Adding an interwiki prefix results in a message being sent to RC feeds that is incomplete. The placeholders are sent without being substituted, for example:
    [[Special:Log/interwiki]] iw_add  * Foo *  Foo added prefix "$4" ($5) (trans: $6; local: $7) to the interwiki table

Steps to reproduce:
1. Create a $wgRCFeed to report changes, e.g.
    $wgRCFeeds['irc'] = array(
        'formatter' => 'IRCColourfulRCFeedFormatter',
        'uri' => 'udp://localhost:3000',
    );
2. Add an interwiki prefix via [[Special:Interwiki]]
3. Observe what is sent over UDP


(Tested in commit df552f8272fc65c4e54edb159e2cd71cd11cf899)