English creative typically performs well in the UAE for expat-heavy or premium consumer audiences and much B2B content, while Arabic — ideally in a dialect the audience actually speaks, not formal MSA — is close to essential for Saudi Arabia and for mass-market consumer campaigns anywhere in the Gulf.
The safest approach for most brands entering the region is running both in parallel and letting performance data settle the split by market and audience, rather than picking one language up front and hoping it covers everyone.