Every single day we use the word "God" which is a Germanic term that goes all the way back to proto-Indo-European paganism. Unless we are prepared to use the word "Yahweh" exclusively in daily conversation, we are going to be using pagan terminology when we are talking about God. The New Testament was written in Greek and uses the word "Theos," which is...you guessed it, derived from paganism. You get that, right?
On that basis, the word "Allah"--which is a term derived from paganism just as the word "God" is--is perfectly acceptable for Christians.
And please keep in mind that the Aramaic word for "God"--a.k.a. the term that Jesus used every day--is Elaha, a close Semitic etymological relative of "Allah."