The LanguageSelector extension [1] can automatically set the interface
language based on browser settings, which is nowadays the norm for
every serious multilanguage web page. It is not used on WMF wikis,
because it would interfere with caching. The strategic planning wiki
[2] has, however, relatively low traffic, and probably much higher
logged-in to anon ratio than the rest of the sites. Any chance
LanguageSelector (or something equivalent, if it exists) could be used
there?
[1]
http://www.mediawiki.org/wiki/Extension:LanguageSelector
[2]
http://strategy.wikimedia.org/wiki/Main_Page