I'd suggest the shortest one, with no .php, aka: mydomain.com/thread/1222-arabic-text-arabic-text-arabic-text
I'd like to expand on this one. I'd remove the
-arabic-text-arabic-text-arabic-text portion, you don't need that long hyphenated URI and it will cause challenges down the line. I might do something along the lines of...
example.com/category/1222
Long hyphenated URIs are not user friendly. If you use them, I'd strongly suggest a shorter counterpart that can be shared easily from memory. You can noindex one or the other, I'd keep the short one as the primary destination page.
Oh, and just because Matt Cutts has long hyphenated URIs doesn't make them the best option for all. Typically those types of URIs are Blog generated. Or, someone saw what others are doing and just followed along not realizing what they were getting themselves into.
From my perspective, long URIs are NOT what you want in the long run. Try telling someone on the phone to go to mydomain.com/thread/1222-arabic-text-arabic-text-arabic-text. You'd be lucky to get past the 3rd hyphen without a typo on the users side.
I'm serious, if you're going to use those URIs for promotion, keep them short and sweet - forget about all the keyword laden hyphenation! Plan your taxonomy, your primary category structure, and then go from there.
example.com/category/1222
Okay, someone tell me what's wrong with the above URI? Remember, the category is going to contain at least one primary keyword relative to that content.
On a side note, if you're doing a major overhaul, now would be the time to get rid of the www. host name, you don't need it anymore. ;)