Is it permissible to use the word "Tanrı" instead of the name "Allah"?

The word "Tanrı" is the Turkish equivalent of the Arabic word "ilâh." Since "ilâh" means "a being that is worshipped," it is sometimes used for Allah the Exalted (c.c.), as well as for beings worshipped by people other than Allah. However, the term "Allah" (lafza-i celâl) is the unique, proper name that specifically refers to Allah the Exalted Himself. In this respect, according to scholars of Islamic theology, the word "Allah" is a special name that denotes the Divine Essence and all His perfect attributes. There is no word in any language that fully encompasses the unique meaning expressed by this term. Furthermore, the word "Allah" serves as a common bond representing the belief in the oneness of God for all Muslims. For this reason, it is more appropriate for Muslims to refer to the one Creator they worship as "Allah." Therefore, Allah should be mentioned by this name or by one of the 99 names known as "al-asmāʾ al-ḥusnā." Nevertheless, expressing the Almighty Allah, who possesses absolute perfection and is free from all deficiencies as described by our religion, with the word "Tanrı" is not contrary to Islamic belief. Indeed, words such as "Hudâ," "Yezdân," "Çalap," and "Mevlâ" have also been used in Islamic societies.

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu