Following an email conversation with Mark Hershberger and Sumana Harihareswara, i request a full-fledged wiki for testing RTL features. Such a wiki is created every now and then as an "Arabic prototype" from the time of the Vector deployment or some such, but the reality is that such wikis are usually not maintained and are neglected after it served some purpose. This new wiki should get at least the same amount of care as test.wikipedia.org.
It may run code from the trunk or something close to it and be used for testing new MediaWiki versions before deployment. It can be used for testing new features, extensions and translations that need special testing in RTL environment.
Just as a reminder, neither translatewiki.net nor test.wikipedia.org can be used for this, because they are LTR wikis, at least until bug 6100 is resolved.
This wiki will be useful for many languages - Arabic, Persian, Hebrew, Divehi and others. If it's possible, then the default interface language for this wiki should be English, but if defining English as the interface language forces LTR directionality, then it should be Arabic - i suppose that it is the RTL language with the highest demand.