In the West, many of us use English as a working language between people of different backgrounds.
The Qurʾān is written in Classical Arabic.
"The holy text is written in Arabic, Islam’s sacred language. For Muslims, Arabic is essential for conveying Allah’s message since it was the language Allah chose. This means that, although the Qur’an has been translated into many languages, only through the original Arabic can one truly know Allah’s message." (Islamic Beliefs and Practices)
which is Islam’s sacred and liturgical language. Because of Arabic’s sacred status, the Qurʾān is, strictly speaking, untranslatable, though the text has been rendered into nearly every other language.
"Most contemporary Muslims are not Arabs and do not know Arabic; also, many Arab Muslims are illiterate. Yet they know passages from the Qur’an. Many Muslims even know the entire Qur’an by heart." (Islamic Beliefs and Practices)