%% You should probably cite rfc6067 instead of this I-D.
@techreport{davis-u-langtag-ext-04,
    number =    {draft-davis-u-langtag-ext-04},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-davis-u-langtag-ext/04/},
    author =    {Yoshito Umaoka and Addison Phillips and Mark Davis},
    title =     {{BCP 47 Extension U}},
    pagetotal = 8,
    year =      2010,
    month =     aug,
    day =       26,
    abstract =  {This document specifies an Extension to BCP 47 that provides subtags that specify language and/or locale-based behavior or refinements to language tags, according to work done by the Unicode Consortium. This document is not an Internet Standards Track specification; it is published for informational purposes.},
}