From Troid.ca, here are Ten reason you want to learn Arabic:
1. Arabic is the language of the Qur'aan
2. The Qur'aan will increase you in intellect
3. The Qur'aan leads to righteous actions
4. The Qur'aan leads to the preceding messages in the previously revealed texts
5. The elaboration upon the Qur'aan is only known in Arabic
6. The great reward for reciting the Qur'aan—each letter
7. Many obligations in Islam cannot be completed except through utilising Arabic (ex. ash-Shahaadah)
8. The Sunnah is recorded in Arabic likewise
9. Without Arabic, a person remains a blind follower of translated interpretations
10. Deviation and innovation often comes from those who do not understand Arabic properly