This property is used to identify data in multiple languages and provides access to undelying LANGUAGE business card or calendar raw property parameter.
For business card v2.1 and v3.0 the language-tag is defined in Section 2 of RFC-1766: http://tools.ietf.org/html/rfc1766#section-2
For business card v4.0 the language-tag is defined in Section 2 of RFC5646: http://tools.ietf.org/html/rfc5646#section-2
The language-tag can be parsed using.NET class.
In case of business card v4.0 the AltId ("ALTID" business card or calendar property parameter) to mark alternative representations of the same propery in different languages.property is used togather with
In case LANGUAGE raw property parameter is not specified, for business card v2.1 this property returns "EN-us" string, that it considered the "default" language. For v3.0 and v4.0 there is no concept of "default" language, except as specified by any "Content-Language" MIME header parameter that is present.