What is the wisdom behind God's creation of peoples differing in languages, while making the Qur'an in the Arabic language, and what is the proof of Islam's authenticity?

The diversity of languages is a testament to the greatness of Allah and His sole right to be worshipped. The revelation of the Qur'an in Arabic highlights its virtue. A Muslim must submit to Allah's decree and be content with it, for Islam is the religion Allah has chosen for His servants. Allah supported His Messenger with clear proofs, such as the miracle of the Qur'an. To escape doubts, one should frequently supplicate, study sound religious books, attend gatherings of scholars, and resist the satanic whispers that may afflict a believer.