Apple Watch issue

Cellular data will probably not work for the Apple Watch model from the US:

...

International roaming with your Apple Watch

With watchOS 9.1 and later, international roaming is available on cellular models of Apple Watch Series 5 and later, Apple Watch SE and later, and Apple Watch Ultra. 

To get international roaming on your Apple Watch, contact your iPhone carrier to add your watch to your iPhone cellular roaming plan. For international roaming to work on your Apple Watch, your carrier must support VoLTE and roaming. Not all carriers support international roaming on Apple Watch and coverage in other countries is determined by your carrier.

To turn on international roaming, open the Settings app on your Apple Watch. Tap Cellular, then turn on Data Roaming.

To cover the LTE and UMTS bands used around the world, cellular models of Apple Watch come in regional models for the Americas, China mainland, and Europe/Asia Pacific. Unlike iPhone, there isn't a worldwide Apple Watch model that supports all cellular bands used globally. Find out which carriers in your country or region offer cellular service for Apple Watch.

...

copied from: Set up cellular on Apple Watch - Apple Support

Apple Watches are built for the country they are sold in, due to the different hardware that might be needed for different carriers or data networks.

So, not all features might work, especially if your Appel Watch has the cellular option.