The Locations... seems to be very poor when you try to add a new location at determining locations' full entry.
As an alternative you can add them to the configuration directly.
- First install dconf-editor.
- Open dconf-editor.
- Navigate to con/canonical/indicator/datetime and edit the locations item with the locations you want.
- UTC UTC
- America/Vancouver Vancouver
- Australia/Sydney Sydney
- Pacific/Auckland Auckland
- Asia/Tokyo Tokyo
- America/Toronto Ottawa