will apple watch 5 work in uk and thailand and turkey

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 above does not list Turkey as having a cellular provider that supports the Apple Watch. Thailand has 3 carriers.

Note: The Apple Watch does not support roaming, so you would either have to get a separate iPhone contract and pay the extra fee to include your Apple Watch so you can share your iPhone's phone number, or you would have to use the Apple Watch as if it was a GPS only model.

If you do use your Apple Watch as if it were a GPS only model, it will do Everything a cellular model will do as long as your iPhone is nearby.

https://support.apple.com/en-us/HT205547

So when you are away from your normally cellular provider, you can still use the Apple Watch and get most features when your iPhone is nearby.

The watchOS feature list is important to review as some services are not available in some countries.

Good afternoon stefsailing,

Welcome to the Apple Support Communities!

I understand you would like to know if the Apple Watch purchased in the UK will work in Turkey and Thailand. The resource below provides the watchOS features by country.

watchOS Feature Availability

Cellular capabilities would depend on the iPhone it is paired with and the wireless carrier plan.

Apple Watch with cellular

Take care.