RTL works just fine on my HD2 without multilang!
It also works well on every app other than SMS..
it seems that only sms fails to set RTL characters to be written from right to left. I can write arabic words, it just they are on the left side of the box other than the right. I can't select a word, and the cursor stays on the left rather than moving with the text.
I've found a workaround though, when I'm writing in arabic, I switch to landscape. RTL works well in landscape, not sure if it's because I'm using a third party keyboard because I've removed the google keyboard.
Not sure about his, but I have an HTC HD2
the language options are the same in both multilang and non-multilang roms.
RTL works just fine in every app in non-multilang, so even if multilang fixes the SMS issue, it's quite bothersome to download another 100+ mb file just to fix a small issue in SMS app..