The strings from RELEASE_FORMATS and RELEASE_COUNTRIES aren't being translated when they're shown in the GUI.
- Open Picard and go to Options -> Options -> Advanced -> User Interface and change the "User interface language" to any language that has country names translated (check e.g. the .po files in Git to verify)
- Restart Picard to make the changes take effect
- Go to Options -> Options -> Metadata -< Preferred Releases
- Compare "Preferred release countries" and "formats" to their translations in the .po of the language you picked