Surah 14:4
"We have not sent any messenger except in the language of his people, so that he might make (things) clear to them. Then God leads astray whomever He pleases and guides whomever He pleases. He is the Mighty, the Wise."
Listeners cannot respond unless they can understand the message. This verse seems to go along with verses that specify that the recitations are in Arabic (e.g., 12.2; 13.37).
- from The Quran with Christian Commentary: A Guide to Understanding the Scripture of Islam