Buying Apple Series 9 watch from Japan for use in Australia
If I buy an Apple Series 9 GPS watch in Japan will it work in Australia pairing with my iPhone 14?
The GPS only models work anywhere your iPhone works. The GPS only does not know, nor care about the cellular carrier of the iPhone. And a Series 9 will pair with an iPhone 14.
Warranties are country specific, so you will not have a warranty in Australia.
You should also go through the feature permitted in Japan vs Australia to see if there are feature restrictions in Japan that would prevent them from working in Australia
watchOS - Feature Availability - Apple