Hi Faheem! "What's up" means that there is a problem somewhere, doesn't it? then in Arabic we say "me almoshkel" or "matha yajri".

what's up ( if you mean what's wrong) =>what's up with you = ma khatboka ( in Arabic) what's up = matha yajrii (th = of mother (eng)) matha = what i think that kaifa alhal = how are you kaifa = how al-hal = the situation

IN ARABIC Y CAN SAY : MATHA HADTH OR MATHA JARA OR MA AL MOUSHKELA

I think what's up is sort of slang greeting, no? as in "hey dude, what's up?" So, it's kinda odd to translate it to standard arabic .. when such statement appears in a movie or a tv show it's usually translated as a casual greeting (marhaban .. etc) do you want it in a specific dialect? I think there are some equivalent phrases ..

what's up=كيف الحال=kaifa alhal