Manual:$wgBetterDirectionality

Experimental better directionality (left-to-right, right-to-left) support.

Details

 * In rev 69185 (1.17), the page lang and dir is in the user language, and a div is added to bodyContent with lang and dir attributes based on the site content language. This means basic distinction between the interface and site content language, instead of marking everything in the site content language (old, default behavior).
 * In ResourceLoader, the directionality was set according to the user language, but this was reverted in rev 81622.
 * In rev 90264 (1.19), it was re-added under $wgBetterDirectionality = true
 * In rev 90265 (1.19), the lang and dir of content div was improved:
 * lang and dir is not set for special pages (those are in the user language)
 * lang and dir of content of pages in MediaWiki namespace is based on the current page instead of site language, e.g. MediaWiki:Message/ar is lang="ar" and dir="rtl"