Standards for codes

Currency codes

ISO 4217 defines codes with 3 latin letters.

http://www.currency-iso.org/en/home/tables/table-a1.html

Official list of currency codes.

https://en.wikipedia.org/wiki/ISO_4217

Wikipedia article.

Country codes

ISO 3166-1 defines 2 letter and 3 letter codes:

• A two-letter (ISO 3166-1 alpha-2).
• A three-letter (ISO 3166-1 alpha-3).
• A three-digit numeric (ISO 3166-1 numeric) code.

http://www.iso.org/iso/country_codes.htm

Official page.

https://en.wikipedia.org/wiki/ISO_3166-1

Wikipedia article.

https://en.wikipedia.org/wiki/Country_code

Wikipedia article.

Language codes

ISO 639 defines several 2 and 3 letter codes for languages.

https://en.wikipedia.org/wiki/ISO_639

Wikipedia article.

https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes

Wikipedia article.