This proposal suggests to use the IANA Character Sets Registry.

I had some concerns about the state of the registry, but I have been
able to register the UTF-7-IMAP charset recently. It may have helped
that it was specified in RFC 3501 in 2003 (but the corresponding IANA
action had been omitted), and it is still in wide use today, without a
deployed alternative. However, the basic process appears to be working,
including MIB assignment.

I can't comment on the feasibility from a ISO process perspective of
using the IANA registry. ISO has its own character set registries,
somewhere in the context of ISO 2022 and ISO 4873. It may be a
nonnegotiable requirement that an ISO standard uses an existing ISO
registry.

Thanks,
Florian

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