For things such as units, we should use formats provided by the International Organization for Standardization (ISO) whenever possible:
- Date/time: UNIX timestamps (in milliseconds) to represent times, and ISO 8601 complete date format to represent dates (iso.org/iso-8601-date-and-time-format.html)
- Currencies: ISO 4217 currency codes (iso.org/iso-4217-currency-codes.html)
- Countries: Either ISO 3166-1 alpha-2, ISO 3166-1 alpha-3, or ISO 3166-1 numeric codes (iso.org/iso-3166-country-codes.html)
- Languages: ISO 639-2 codes (iso.org/iso-639-language-codes.html)