iso.org is the entity that assign entities for maintenance and registration authorities for various standards. You can find the list and their websites here: https://www.iso.org/maintenance_agencies.html
Source: https://www.iso.org/mara/iso3166
Source: https://www.loc.gov/standards/iso639-2
Source: https://www.six-group.com/en/products-services/financial-information/data-standards.html