Package langreg is a library for validating ISO 639-1 language and ISO 1366-1_alpa-2 region codes.
ISO 639-1 language codes are two charcters long and use only lowercase ASCII character a-z. E.g.:
"en", "es", "ru"
ISO 1366-1_alpa-2 region codes are two charcters long and use only uppercase ASCII character A-Z. E.g.:
"US", "UK", "ZA"
When combined as a composite language and region code, they are concatented with an underscore. E.g.:
"en_US", "en_ZA", "fr_FR"
Any codes not meeting these formatting requirement will fail validation.