locale name for sub-country dialects?

[Robert Millan]

Hi!

How should sub-language dialects that, instead of matching a country
(ISO-3166-1), match a sub-country (ISO-3166-2) division, be specified in locale
values?

POSIX (XSI) reads:

<quote>
If the locale value has the form:

language[_territory][.codeset]

it refers to an implementation-provided locale, where settings of language, territory, and codeset are implementation-defined.
</quote>

Do we handle this with ISO-3166-2 codes, or are generic @something modifiers
preferred?

And in case @something modifiers are preferred, do we use the name of the
language variant in English, or in the local language itself?

Thanks,

-- 
Robert Millan