Changed language field to adhere to RFC 5646

[seanherron]

As mentioned in http://dublincore.org/documents/dcmi-terms/#terms-language, language fields should adhere to a controlled vocabulary such as RFC 5646. I've updated the schema to reflect that. I'm assuming documents in multiple languages should just be comma separated, though if I missed a place where the standard defines a better way to do that please edit accordingly.

[MarinaNitze]

I always like adhering to controlled vocabularies -- but this needs more fleshing out in the guidance. Maybe with an example of the English and Spanish values (which, I assume, are the two most common)?

[seanherron]

I added some additional examples and guidance per your suggestion

[MarinaNitze]

Is RFC 5646 preferable to only ISO 639-1? Just confirming.

[seanherron]

I prefer it since it shows differences in regional dialects, such as British English to American English, and matches Dublin Core.

[benbalter]

👍

[MarinaNitze]

Accepted into the final 1.0 schema being submitted internally for approval. Thanks Sean!