FOLIO uses a specific list of codes for countries.
The list is difficult to find, so:
Start at the Stripes Components README, and follow to the CountrySelection component.
Its CountrySelection.js file imports the higher-level util/countries.js which has each entry for the two-letter and three-letter alphabetic codes, and the numeric codes.
The translations/stripes-components/en.json has the default names in English language, and of course there are the other translations.