Mediawiki provides no real support for truly multilingual wikis at all. Despite the fact that the prominent multilingual wikis Commons and Meta are around since 2004 and 2001 respectively. Making Mediawiki truly multilingual is a heavy task. There are at least a dozen things that come up in my mind where Mediawiki sucks multilinguality-wise. But a simple first starting step would be to create a global variable like "$wgMultilingualWiki = true/false" and if it is set to true the content language will automatically be set to the language set in the preferences. That will remove several problems like the wrong tab order for RTL languages or the fact that {{PLURAL: }} doesn't work correctly for any language with a different plural structure than English.
Marcus Buck User:Slomox