The document reference RFC 3066 for language tags.  The work in LTRU on changes to the registry and registration guidelines managed by BCP 47 should be of interest to the author and the RFC Editor staff in this context, and I suggest that the author consider the current drafts in LTRU when describing the registry.  The mechanisms for defining the role of subtag in a tag may be of use in this context. 

It's not clear what "Whois file" is meant to include in the Security Considerations, and a more complete reference would be valuable.

It might be valuable to include more detail related to the consequences of different actors 
developing the  registration bundle.  In one model, the registrant creates the whole bundle--
the string intended for registration, the languages of intended use, and the the variants.  In
other models, the registrant might populate  only the string intended for registration and the
languages; in yet others, a registry may restrict the language intended for use according to
local policy.  There are significant differences in the ability of registrants to accidentally
fail to use the registration process correctly or, indeed, to intentionally game it under different
policies about who develops the registration bundle.