try like below.
System.Globalization.CultureInfo ci = new System.Globalization.CultureInfo("ar");
System.Threading.Thread.CurrentThread.CurrentCulture = ci;
"ar" specifies, its arabic. Its the culture name for arabic.
the above code will create the new culture and that will be added to your thread. in your case will be suitable, the culture is active till the thread exists.
hope it helps.