Only a relatively small percentage of Muslims speak Arabic as their first language, yet Muslims around the world use the same word for God: Allah. But why? Why not just use the word for God in our own languages? One reason is that, since the Quran was revealed in Arabic, and Arabic is used by Muslims multiple times a day in prayer, the word has something of a unifying quality for Muslims. No matter where we're from, no matter what language we speak, Allah is one word we can all understand. While there is nothing wrong with using other words for God, most Muslims are accustomed to using the word Allah, and many prefer to use the word Allah over the word for God in their own language. However, a deeper reason that many cite is the unique quality of the word Allah. Look at English word God. We spell it with a capital G and it means the One True God, but make it a lower case g and it could be referring to Zeus, Ganesh, Thor, or anything that people worship. Since capitalization does not come across in speech, there is no way to distinguish between God and... god. If you add an s it becomes gods plural, and it can become male or female, god or goddess. In contrast, the Arabic words for god and God are two different words. Lowercase god is ilah and capital God is Allah, so when you say Allah there is no confusion. On top of that, the word Allah is unlike most Arabic words in that it cannot be made plural nor take gender. So when you say "Allah" there is no doubt that you are talking not about one of many gods, but about the One and Only God, not a man or a woman but the Creator of men and women, capital G-o-d, God.
"And to Allah belong the best names, so invoke Him by them."