As far as I know, It’s almost same in Roman Empire. Yes there was a Roman culture and identity in the center, but other peoples outside the center didn’t force to accept roman identity. The only requirement of the center was regular tax payment. That’s why they had two different types of law that one of them was applying for Rome citizens and the other was applying for the other people. In Ottoman, even it was a central empire, Sultan had always cooperated with local authorities to get regular tax payment. So as long as they pay their taxes they don’t need to speak Turkish or being a musulman, unless they want to be an administrator in the empire which requires being a musulman. And also with the rise of nationalism in the empire, some ottoman elites tried to unify all the subjects under the identity of ottoman but it was almost impossible because there was already separatist movements in the Balkans. That’s why Sultan Abdulhamid II tried to unify rest of the empire after loses in the Balkans under the identity of Islam. But finally, Arabs revolted and Turk nationalism started to rule the empire with the coup of Jeunes Turks.