Correct locale for non-national languages?

[Charles Voelger <cvoelger dweasel com>]

locales are ussually lang_COUNTRY as in en_US or en_GB, but what is the
correct format for an 'international' language such as esperanto?

I have seen eo_EO - but this seems wrong to me as EO is not an ISO
country code, and shouldnt be confused as such.  I've also seen eo_XX
but that just seems sloppy to me.

Is there an approved way of doing this?  Should one make seperate
locales for different countries, so we'd have eo_US, eo_DK, etc etc? Or
would it be best to just have "eo" and leave the "_COUNTRY" off?

-- 
Charles Voelger <cvoelger@dweasel.com>