UPDATE 1-Regulator backs ADIB purchase of Barclays UAE unit - CEO

* Transfer of Barclays UAE customers to start Sept 1 - CEO* Studying whether to pursue buys in SE Asia* Tentative agreement reached on Amlak restructuring* Proposal to extend time on Amlak debt repayments(Adds details, context)By Stanley CarvalhoABU DHABI, May 20 (Reuters) - Abu Dhabi Islamic BankADIB.AD has received regulatory approval from the United Arab Emirates central bank for its purchase o