Ok peeps, for those who want to guinea pig it:
1/ Select the SMF Default Theme - in the theme change thingy in the bottom block of the left column (under Recent Posts). This theme is really boring. It's so boring Hass likes it.
However it does come standard with CSS for supporting RTL languages (like Arabic).
Our sexy custom themes don't come with rtl.css, which means some wally (ie: me) is going to have to write it. That aint happening overnight.
Anyway you can change back from the boring one to whatever you like anytime, but just remember the sexy ones will probably look pretty messed up if Arabic is selected in your profile.
2/ Go to Profile > Account Related Settings > Preferred Language: and choose whichever one you want to use. You'll have to enter your password to save the change which is a PITA. Should be able to change that fairly easily so passwords aren't needed, but until some recoding is done that's the best we can do.
Try it out and see what happens. Be warned that if you try this without being able to read Arabic it may do your head in.