It is better to refer to BCP-47 instead.

https://tools.ietf.org/html/bcp47

An RFC can be updated, when it is, it recieves a new number. For language
tagging, the relevant information is split across two RFCs. BCP-47 is a
permanent IEFT ifentifier referencing the latest versions of the two RFCs
relating to language tagging.

Andrew

On 2 Jun 2016 9:24 am, "Stuart A. Yeates" <[log in to unmask]> wrote:
>
> I recommend reading https://tools.ietf.org/html/rfc5646 which seems to do
> what you need.
>
> cheers
> stuart
>
> --
> ...let us be heard from red core to black sky
>
> On Thu, Jun 2, 2016 at 10:59 AM, Greg Lindahl <[log in to unmask]> wrote:
>
> > Some of the Internet Archive's library partners are asking us about
> > language metadata for regional languages that don't have standard
> > codes.  Is there a standard way of dealing with this situation?
> >
> > Overall we use MARC codes https://www.loc.gov/marc/languages/ which
> > were last updated in 2007. LOC also maintains ISO639-2
> > https://www.loc.gov/standards/iso639-2/php/code_list.php last updated
> > in 2014.
> >
> > The languages in question are regional languages which are currently
> > lumped together in both standards. With the recent rise in interest
> > and funding for regional languages, it's no surprise that some
> > catalogers want to split these languages out into separate codes.
> >
> > Thanks!
> >
> > -- greg
> >