Is Allah in the Quran the same God as YHWH in the Bible? God in the Bible is not the same character or personality as God in the Quran, and there are major contradictions between them theologically. However, Arab Christians call God, Allah, not because they believe Islam has the same God theologically, but because Allah means the[one] God in Arabic. The Arabic-descended Maltese language of Malta, whose population is almost entirely Roman Catholic, uses Alla for “God”. The Aramaic word for “God” in the language of Assyrian Christians is Elaha, or Alaha. A German speaker wouldn’t say God either, they would say Gott, which is where English gets its word God because English is a Germanic language. Nor would a Spanish speaker wouldn’t say, God, they would say Dios because that is God in Spanish. They are just the words for the classification of a deity, similar to how words like El-Shaddai or Adonai (the Lord) in Hebrew function as the title of Lord, or God Almighty, but these are not necessarily the name of God, like YHWH. Likewise, the new testament is translated from Greek, which uses the word Theos (Θεός). Paul didn’t make Greeks stop saying Theos and switch to Adonia, so I don’t believe it’s necessary for Arab Christians to use something other than Allah.

What does the Arabic bible say? Does it say “God”? No, it doesn’t. In an Arabic bible, it says Allah (اللهُ) because the language is Arabic. Where in the bible did Jesus say “to teach all nations but they have to learn English, Greek, or Hebrew language first”? The Arabic bibles say, Allah, because of linguistics, not theology. So it makes no sense for them to use a word unfamiliar to their language. It’s like saying we English speakers can’t say “God” because the English bible is not the original language, and we have to say Adonia. It’s the same argument as, “We can’t say Jesus we have to say Yeshua/Yahshua, because Jesus is a ‘pagan name’.” Jesus is “Isa” in Arabic, so an Arab speaking Christan proselytizing to an Arabic speaking non-Christian will say “Isa is the Masih” (Jesus is the Christ), and that is biblically correct because the language has the same meanings as the bible.

There are missionary ministries that are translating the Bible into indigenous languages around the world, so is it wrong for new Bible translations to call God whatever word an indigenous culture uses for “god” in their language? Again the New Testament authors had no problem using Theos because they didn’t maintain Adonia in the Greek translations of the New testament. Christos (Christ) is the Greek equivalent of the Hebrew “Mashiach” (Messiah), why do we use Christ then if we are supposed to stick with one language?

Any Bible-believing Christian that knows what the Quran says about God’s personality and character would reject it, however, the language of Arabic pre-existed the religion of Islam, so we must not equate the two. Arab speakers were there in the book of Acts 2:9-12 when the Holy Spirit was distributed to those in the Upper Room, so the language of Arabic is not anti-christ. Islamic theology on the other is classified as antichrist according to 1 John 4:2-3. We can translate the gospel to other languages for the sake of the great commission without syncretism with the religions of those cultures. our word “hell” comes from Helhiem the afterlife in Norse mythology. Does that mean the English-speaking Christians are practicing nordic god worship when we say it? No, all the days of the week and the first 6 months of the year in western European languages are named after Greco-Roman or Norse gods. Every language outside of Hebrew comes with words that have other uses for other beliefs, the words themselves are not evil because other religions use them. More on the translation of Hell here.

This writing is targeted at the western Christians who say “Allah is not God” as an aggressive phrase targeted at Arab speakers because they assume all Arabs are Muslim. To further my point, English-speaking westerners involved in New age pagan practices, often talk about a god but they aren’t talking about the biblical God. Yet they still use the same word because it is English. Should English-speaking Christian stop saying, God?

In conclusion, Arab-speaking Christians are going to use their native word for God, Allah. When people say God in English they are typically referring to YHWH, the God of the Bible. Ilah is the equivalent of saying “god” (with a lower case g), in Arabic. However, Allah is in reference to the Abrahamic God. The English translations of the bible use God instead of god when referring to the God of Abraham. Same thing with Allah and ilah. There are no capital letters in Semitic languages, that’s a western thing. So they distinguish between god (generic usage) and “The” God of Abraham by putting an equivalent of “the” in front. The Al in Allah, Allah can be translated to the word “the” in English. For example, Algebra is derived from the phrase “al-jabr” meaning “The reunion of broken parts”. It was the name of a book written by Muḥammad ibn Musa al-Khwarizmi, the 8th-century polymath scholar who invented “Algebra” (al-jabr) and also introduced the western world to Arabic numerals. In fact, his last name al-Khwarizmi is Latinized as algorithmi, which is where we get the word algorithm.

Examples:
Gen 1:1 In the beginning God created the heavens and the earth
Gen 1:1 in Arabic: فِي الْبَدْءِ خَلَقَ اللهُ السَّمَاوَاتِ وَالارْضَ.
Notice it uses Allah (اللهُ) for God, this is from the Coptic bible.

Deut 18:20 But any prophet who falsely claims to speak in my name or who speaks in the name of another god must die.

Deut 18:20 in Arabic:
وَأمّا النَّبِيُّ الَّذِي يَتَجَرَّأُ أنْ يَدَّعِي أنَّهُ يَتَكَلَّمُ بِاسمِي وَلَمْ أُوصِهِ بِشَيءٍ، أوْ يَتَكَلَّمُ بِاسْمِ آلِهَةٍ أُخْرَى، فَيَنبَغِي أنْ يَمُوتَ ذَلِكَ النَّبِيُّ.
Deut 18:20 uses the phrase alihat ukrah(آلِهَةٍ أُخْرَى،) for another god (false god).

Resource:
More info on God for Arabic Christians