xs:language
Elements and attributes with type xs:language contain a language code as defined in RFC 1766,
Tags for the Identification of Languages.
These are essentially the acceptable values for the xml:lang attribute described in Chapter 5. If possible, this should
be one of the two-letter language codes defined in ISO 639,
possibly followed by a country code. For languages that aren't
listed in ISO 639, you can use one of the i-codes registered with
IANA. If the language you need isn't present in either of these
sets, you can make up your own language tag beginning with the
prefix "x-" or "X-". Thus, these are acceptable language
values:
en
en-US
en-GB
fr-CA
i-klingon
x-quenya
X-PigLatin
Constraining facets that apply to xs:language are length, minLength, maxLength, pattern, enumeration, and whiteSpace.