Currently xml:lang is set by $wgContentLang only. It's not good to search engines to determine the real content language of a specific page. The worse thing is, Wikimania 2007 site set xml:lang incorrectly to "wikimania2007".

By helps from Ping Yeh ping.nsr.yeh@gmail.com, the patch checks available language codes of Template:Languages to set xml:lang dynamically. It's particularly important to http://wikimania2007.wikimedia.org or other sites used Template:Language to retain the impact of search engine optimizations.

Please refer to http://bugzilla.wikimedia.org/show_bug.cgi?id=10736 for the patch. Thank you!

Cheers, /Mike Tian-Jian "b6s" Jiang/