xml:lang - Languagetypes available as modular xsd-file?

Hello everybody,

one question about using standardized language-codes in XML:

 I would like to use the standardized Iso-language terms in my XML-Schema. I know that
there is an attribute-name "xml:lang" and in the modular HTML-xsd I saw
that the type of xml:lang is definied as a languagetype, which is just an
NMTOKEN.
Is there a standard module with an entity-set or enumeration list with all
language- and country-codes,that I can include? I am also interested in standardized currency-codes and using them in XML.

Thank you very much for your attention!
Best regards
Inga Eckermann