The immediate audience of the Messenger of God ﷺ was the Arabs living in Makkah. The Majestic Quran is guidance for faith and practices and it is obvious that this has to be in the language of the people. The Arabs were amazing poets and cherished their poetry, however, the Quran was not poetry, although it was in beautiful and eloquent prose, the Arabs found it very impressive and unique. The Quran claims “these are the verses of a clear book. We revealed it as an Arabic Quran so you may understand” (Yusuf: 1-3).
The Quran is only in Arabic. This does not mean that it cannot be translated, but the translation is not the same thing as the original text, its an interpretation of it. We know that previous revelations were sent in the language of their people.
One of the beauties of the Arabic language is that it has a very complex system of grammar and word-formation. One statement can mean many things and this is only possible in the Arabic language. Arabic is syntactical, which means it cannot be compared to any other languages in terms of grammatical rules making it unique.