Hi,
I usually don't post to mailing lists, but Brion suggested I should do this for the page content language.
I suppose most people now that I improved the RTL support. Documentation of that is now at http://www.mediawiki.org/wiki/Directionality_support If it is incomplete or unclear about something, please ask so I can improve the docs.
While doing that, I introduced a "page content language" that defines the language in which a specific page is written. I added docs for that as well, see http://www.mediawiki.org/wiki/Language_in_MediaWiki For special pages it is $wgLang, for MediaWiki namespace pages it depends on the subpage code, for other pages it is $wgContLang. Extensions (like Translate) can change the language a page is supposed to be written in. This affects the direction of the content, the TOC, and (in theory) the grammar. Again, if the docs are missing something important, let me know.
But, now that I am writing this anyway, I have a question: should magic words like CURRENTMONTH and NUMBEROFARTICLES use the page content language rather than wgContLang? It would be more logical (and on Incubator even wanted: http://incubator.wikimedia.org/wiki/Template:Wp/lkt/CURRENTMONTHNAMEI ) but I am not sure if it would break things, e.g. when just with a template.
(And btw, another i18n thing that needs attention is LanguageConverter (even just for missing docs). I am looking if I can help out there.)
Regards, Robin aka SPQRobin