Try reading post 80. What we’re talking about here is the difference between the reality and the word that refers to the reality. The map vs. the territory if you will.
The Allah of the Koran and the God of the Bible are certainly not the same person.
However, the Allah worshipped by Arabic-speaking Christians and the God worshipped by English-speaking Christians is the same.
Why should Christians agree that only Muslims can use a word that Christians used for centuries before Islam existed?
Christians worship one God, no matter what their nationality is—Arab, Chinese, Indian, whatever. There is one God and one way to Him: Jesus. That’s all.