Like others, Arabs also write Arabic with their right hand. There are some exceptions.
Some people write with their left hand all languages.
I am a non-Arab, but I use my left hand to write Arabic. It was not by choice but by chance.
Due to an accident, my right hand become inactive. I started to write with left hand. Still I write
with it all other languages also, although my right hand is very active now and without any weakness.