As an Arab, for me the use of the Word "Allah" is only the arabic translation of God. So why create the distinction of the 2 words? I have read somewhere that this idea of using the word came from orientalists that made sure to differentiate "Allah" and "God" to distinguish the 2 as if they're different.
Bismillah. Asalam mu alaikoom.
"Allah" is different to the word "God" in many ways.
1) Allah means "Al Ilah" Al for "The" Ilah for "God." So Allah means "The God" and the Pre-Islamic Arabs who were polytheistic had other "gods" beside Allah but Allah was known as the Immaterial God - they (the pagan Arabs) recognised Allah swt as Al -Khaliq (The creator) but refused him as their "Rabb" (Lord).
So, in reality Allah is the immaterial unseen God.
2) Unlike in English the word God can be changed into "gods" "goddesses" "demigods" etc.
(i) Whereas Allah despite being in a language which like spanish etc. has feminine and masculine (is a gender based language), the word cannot be made into either of these genders and is genderless. Subhanallah!
(ii) Also the word Allah cannot be made into a plural, and therefore, in the arabic languages there are two words for God: Allah - the immaterial God and Ilah - "god(s)"
3) Allah know best but i've heard that there is uniqueness to the word Allah itself. In arabic, you can break down letters further.eg. A'yn becomes A'yn, yaa and noon. Allah knows best but I heard that the pagan Arabs tried making jokes with Allah's name so they tried breaking it down but it didn't really work...
(Also, in English you can break words into smaller pieces too: these are morphenes and can be broken down into a word's linguistic meaning and grammartical meaning)
So in reality, when we compare the word "Allah" to "God" we find "Allah" to be more unique and of a befitting nature to Allah itself.
FUN FACT: (for the reasons above - i.e. the uniqueness of "Allah") the bible uses the word "Allah" for God instead of "Ilah" when it is translated in Arabic.
In english interpritation of the Holy Quaran Allah is frequently called God (for example, al-Baqara, 162, "Your God is One God"). So there must be no problem is you, as a speaker, refer to Allah by the word "God".
But one should keep in mind that a listener can misinterpret them, especially if a listener does not know that speaker is a muslim or if someone, for example, has a conversation with a christian.
The word allah is unique you cannot have more than one Allah only one Allah for example the word Allah's cannot be used. So when the word Allah is used you know it refers to the one and only creator. On the other hand the word God is not unique it can be said as god's for example the Greeks God's and so when the word god is used it is unclear as to which God is being mentioned. Is it the Hindu God or the Greek God or the Muslim God?