To answer this question, you first need to understand what the Quran is and how it is viewed by most Muslims.
As we mentioned in our brief biography of Muhammad, the Quran is the written record of every revelation received by the Prophet Muhammad from Allah through the angel Gabriel. It's essentially the transcript of a one-sided conversation between Allah and his prophet. And as such, it is viewed by Muslims as the unerring, unchangeable word of God. While some verses, such as those prohibiting alcohol or pork, have a defined interpretation, there are others that are less clear.
Let's compare that to the Old and New Testaments of the Bible. While the Old Testament contains some direct quotations from God, such as the recitation of the Ten Commandments in the Book of Exodus, it's also considered by many to be an historic chronicle of a people. The four gospels of the New Testament (the books of Matthew, Mark, Luke and John) are likewise presented as third-person accounts of Jesus' ministry. And while some Orthodox Jews and devout Christians claim that the Bible or the Torah are the inerrant words of God, many others believe they are inspired documents open to interpretation.
The Quran was originally written in Arabic, the language spoken by Muhammad and his early followers. Since Muslims believe the Quran to be the direct word of Allah, the holiest and most correct version of the Quran is in Arabic. While the Quran has been translated into hundreds of languages, the original Arabic is still used in prayers and religious services, much like Latin and Hebrew are the default liturgical languages in many Catholic and Jewish congregations [source: ING].
For non-Arab Muslims who want a deeper understanding of the Quran, there is no prohibition against reading the scriptures in translation for personal study.