The software update may have restored your phone to it's original settings, including the language. You should check the language options in the phone, for example via Menu > Settings > Phone > General > Phone language. If the Arabic language is available, select it.
If you are still unable to reselect the Arabic language and think that you should, please visit your nearest Nokia Care Point.
To avoid the problem, always make sure to purchase your Nokia phone from an authorized Nokia retailer in your home country.