An RFC 1766-style language tag, with all alphabetic
characters converted to lowercase. This restriction is
intended to make the lexical ordering imposed by SNMP useful
when applied to language tags. Note that it is
theoretically possible for a valid language tag to exceed
the allowed length of this object, and thus be impossible to
represent in this table. Sampling of language tags in
current use on the Internet suggests that this limit does
not pose a serious problem in practice.