In due course, we should install the relevant ISO 2- and 3-letter codes as the enumerated possible values . . .
Source
<xs:complexType name="shortLocalizedStringType"><xs:annotation><xs:documentation>A short string-valued text designed to be able to fit into a single varchar type field in a database.</xs:documentation></xs:annotation><xs:simpleContent><xs:extension base="metobj:shortStringType"><xs:attribute ref="xml:lang" use="required"/></xs:extension></xs:simpleContent></xs:complexType>