The IANA Registry for IDN Language Tables was created to support the development of the IDN technology.
Specifically, as described under Guideline 3 in the Guidelines for the Implementation of Internationalized Domain Names (IDNs):
In implementing the IDN standards, top-level domain registries will (a) associate each registered internationalized domain name with one language or set of languages, ...and, (c) where the registry finds that the registration and administration rules for a given language would benefit from a character variants table, allow registrations in that language only when an appropriate table is available.
In addition to making the Language Tables publicly available on TLD registry websites, the TLD registries (TLD Sponsors, gTLD and ccTLD Registry Operators) may register Language Tables with the IANA, which in turn will display them online for public access.