Comment by malikolivier

It should be noted that only Modern Standard Arabic (the modern common Arabic language based on the language used in the Qur'an) still has dual. Most (if not all?) spoken dialects, which evolved from this form of Arabic have already lost dual.

It's interesting that we notice a similar pattern of losing the dual in many languages. And it would be very interesting to find the opposite pattern: a language where the dual newly develops out of nowhere. However, I do not know of such language.