Is it permissible to use the word “God” instead of the word “Allah”?
The word “God” is the equivalent of the Arabic word “ilah”. “Ilah” is rather used for beings that are considered as worthy of worship other than Allah. The word “Allah” is a special name which expresses Himself (swt) in person. In this respect, according to the scholars of Islamic theology, the word “Allah” is the special name referring to His supreme personality and all His perfect attributes. There is no other word in any language to cover its special meaning. On the other hand, the word “Allah” is like a common bond that represents the belief of tawhid for all Muslims. Therefore, it would be more accurate for Muslims to call their only creator, to Whom they worship, as “Allah”. Therefore, “Allah” should be remembered with either this name or one of His 99 names called “al-Asma al-Husna”. However, calling Allah, Who has the absolute perfection as informed by our religion, and is free from any deficiencies, as “God” is also not contrary to the Islamic belief.
Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWAS