UAE/Dubai have not approved ECG, so until they do you will not be able to use ECG, even if you take the Apple Watch to a country that has given approval. The ECG rule is the government of the country where purchased must approve AND the government of the country where used must approve.
Apple Watch ECG countries
https://www.apple.com/watchos/feature-availability/#branded-ecg
22 years or older
Walkie-Talkie will not work, as it is based on FaceTime and FaceTime is restricted by the UAE/Dubai government.
Apple Watch Walkie-Talkie countries
https://www.apple.com/watchos/feahttps://support.apple.com/en-us/HT205547
Oh yea, you may have warranty issues trying to get an Apple Watch serviced outside of the country/region where it was purchased.
There are 2 Series 5 cellular radios. The North American (Canada, U.S., Mexico, Puerto Rico) and the Rest-of-the-World. So if you are not talk the Apple Watch to one of the North American countries, it will work.
The Cellular Apple Watch shares the iPhone's phone number. This requires the iPhone cellular carrier to support the Apple Watch. The iPhone carrier charges a monthly fee for this service. In the U.S. the fee is $10 per month added to your iPhone bill.
iPhone Cellular Carriers that support the Apple Watch, which models, the radio frequencies each model uses, and the country where they offer service:
https://www.apple.com/watch/cellular
The GPS only Apple Watch can do Everything the cellular model can do as long as your iPhone is nearby, where nearby is somewhere in the same 3-4 bedroom home (assuming typical wood frame construction).
https://support.apple.com/en-us/HT205547
The Cellular Apple Watch allows you to leave your iPhone at home while you go for a walk, run, bike ride, etc...