Tl;dr: The takeaway here is to install the SuicaEng app on your iPhone. Use the regular Suica app if you read Japanese and/or need advanced features.
Region Settings and Apple Pay - Ata Distance:
The iOS Region Setting and Apple Pay are linked together in interesting ways that has changed with iOS versions. Up through iOS 10, devices needed to have the Region match the country they wanted to add and use cards in: iPhone had to be set to Japan to add and use Japanese credit cards in Apple Pay, and so on.
This was a pain when I first came to Japan.
This changed in iOS 11 with global FeliCa iPhone and NFC switching. The Region setting only needed to be changed to add a card for any particular country and had nothing to do with using it. This is because Apple Pay Wallet only displays the card options that match the Region setting and acts like a filter …
After adding a card, the Region setting can be anything as Apple Pay ignores it and takes care of the rest.
This was wildly unintuitive. I discovered it on accident when I set up my new iPhone.
Many inbound users don't realize this and have avoided adding Suica to Apple Pay under the misconception that the iPhone/Apple Watch Region has to be set to Japan to use it.
…as one would expect.
Wallet behavior is the same in iOS 12, even with the iOS 12.2 UI tweaks, but the Region setting can be completely ignored when adding cards to Apple Pay with an app like SuicaEng. SuicaEng simply adds Suica no matter what the iPhone Region setting is, a nice time saver because changing the iPhone Region is a mini restart.
The SuicaEng app is almost perfect. It provides just enough functionality for 95% of Western travelers if they read English - and they don't need to be able to read much at that.
Another small change from iOS 11 is that if you have a Suica card deleted from Wallet that is parked on iCloud, Wallet will show you the Add Suica option no matter what the iPhone Region setting is. It's a nice touch and reminder in case you ever forgot you had one.
This is valuable when swapping devices or when troubleshooting issues.
I hope there is either more advanced functionality coming in the SuicaEng app or English language support in the full Suica app. As it is, with a little help from my friends I can get what I need out of the Suica Two-Step.