The short answer is that the non-cellular version will work anywhere the paired iPhone can work. The cellular version is not supported yet in UAE or Bulgaria so it would fall back to behave like the non-cellular version.
The list of current celluar support is Apple Watch - Carriers - Apple and you should remember that the cellular function is available only when the watch is activated on the same cellular account as it’s paired iPhone. In other words it is pointless for you buying the LTE version at this time because the cellular service will not be available to you. The non cellular version Apple Watch Series 3 with GPS will work perfectly with your iPhone anywhere in the world.
For the LTE version which is not currently supported in UAE you should be aware that any cellular versions you find available will be unofficial grey imports so (a) there may be no warranty from Apple, and (b) you don’t know which regional variant you are buying. You will see from the carrier list I linked above, Apple has 3 regions each supporting different LTE bands. If you hope to use it when cellular support becomes available in Bulgaria it is critical you get the correct version.
Even if you buy from an official approved Apple source in UAE you should check whether Apple warranty will be respected when the watch is exported. In most regions the warranty is geographically restricted to the area of supply.