Hey there Ahmadov550,
Thanks for reaching out to Apple Support Communities. I understand you have some questions about the difference between devices purchased in the US and UAE. I’ll be happy to help.
The FaceTime app may be affected on devices purchased in Saudi Arabia, not necessarily the UAE, you can read more about this here:
Get help with FaceTime on your iPhone, iPad, or iPod touch in Saudi Arabia
There can be other differences. One thing to pay attention to is the cellular version of Apple Watch. ‘To cover the LTE and UMTS bands used around the world, there are two separate models for Apple Watch Series 5, and three for Apple Watch Series 3. They have been optimized for use in the country of purchase, and not all models work in all countries or regions. There is no single model that supports roaming worldwide. To see which carriers in your country or region offer cellular service for Apple Watch, refer to this link:’
Apple Watch - Carriers
You’ll also want to be aware that if you purchase a device from a different region, the power supply may be different. In this case, it may be a good idea to get the Apple World Travel Adapter Kit:
About the Apple World Travel Adapter Kit
Also, with items like Mac computers, the keyboard may have a different language on the physical keyboard.
Before making a purchase, it may be a good idea to reach out to Apple Sales Support for further help:
Contact - How to Contact Us
Regards.