The Arabic broken plural has the effect that scholars still debate how to properly classify the several branches of Semitic languages.
The correct vowel endings damma, kasra, fatha in Arabic can be a headache. If you are careless, you could turn verse 9:3 of the Qur'an into blasphemy (kufr).
The question of the wasp or hornet - Masʾala(t) al-Zunbur (مَسْأَلة الزُّنْبُور) - caused Sibawayhi, the most famous Arabic grammarian, to die of anger.
Yes, there are one-letter-words in Arabic. You probably know the word for and وَ. But there is more - the imperative.
Actually, I don't think that anybody has ever counted the number of Arabic roots. Mathematically: 21,952 roots. Practically, you get 6,332 roots.