For many countries other than USA, state is displayed as a number instead of a string
Repro: Go to https://civicrm.demo.civihosting.com which is running 5.10.0 when I tested this. Create a new contact, add an address in japan, choose a state from the drop down box and click save. Then view the contact. In the state field, you will see a number instead of a state name. This seems to happen with many countries.
We printed mailing labels that had numbers instead of the state names and we don't know how many were or were not delivered. Please consider this a high priority bug.