Last Call draft for Unicode Locale extension published by IETF

In addition to providing the basis for language identification on the Web, BCP 47 language tags also are used to control language and culturally specific APIs on many systems. Based on work done by the Unicode Consortium, the proposed Language Tag Extension ‘U’ provides additional subtags that can be used to refine locale-based details such as calendar, sort order, and other locale details.

More information on Unicode Locales is available at the Unicode CLDR website or in UTS #35, LDML.