Proposed resolution:

Change footnote 253 in [locale.moneypunct.virtuals]:

²⁵³⁾ For international specializations (second template parameter true) this is always typically four characters long, usually three letters and a space.

[locale.moneypunct.virtuals], para 4 footnote 257 says

²⁵⁷⁾ For international specializations (second template parameter true) this is always four characters long, usually three letters and a space.

The following objection has been raised:

The international currency symbol is whatever the underlying locale says it is, not necessarily four characters long.

[Plum ref _222632Y41]