As I understand it, we simply need someone to keep the LanguageAr.php
file up to date to localize the relevant keywords. When MediaWiki
provides the _functionality_ to localize something, but it is not
localized because a volunteer hasn't done it, it isn't MediaWiki that
is broken. We just need people to maintain the language files in each
language; whether it's LTR or RTL is irrelevant. This process can of
course be expedited by paying someone to do it.
As for distinguishing between minor annoyances and things which are
"horribly broken", I'd like to see some surveys among the actual users
of the various non-English Wikipedias. As things are, I am entirely
unconvinced that it is RTL issues which are the cause of the fact that
has "only" 12000 articles. Limited access to or use
of the WWW would be a much more important factor.