Pages in non-Special namespaces in some wikis using the RTL interface (examples below) have a very large width, which makes a horizontal scrollbar to appear. This happens with many browsers (Chrome, Firefox, Safari, ...) and many OS's (Mac OS, Windows, ...).
Here are a few examples:
http://ar.wikipedia.org/wiki/نابليون_الأول
http://fa.wikipedia.org/wiki/ناپلئون_بناپارت
http://fa.wikibooks.org/wiki/آموزش_زبان_انگلیسی
http://mzn.wikipedia.org/wiki/تبرستون_علویون
I can see the same problem in other projects in following RTL langauges: fa, mzn, ar. I haven't been able to reproduce it in Hebrew wikis of Wikimedia. Given that multiple projects are affected, it looks like a MediaWiki-level CSS-related bug.
Version: wmf-deployment
Severity: major