New file format uses ISO 639-2 alpha-3 plus TLDs, ignores BCP 47

Phillips, Addison addison at
Tue Jul 12 20:58:22 CEST 2016

One other point: the reference BCP47 is stable over time, whereas RFCs can be obsoleted. While there are no plans currently to update RFC 5646 and while great pains are taken to maintain compatibility of language tags in any revision, it certainly could happen at some time in the future. In an ID, you might prefer to reference the RFC. But at W3C and in many other contexts we generally recommend referencing BCP 47.


Addison Phillips
Principal SDE, I18N Architect (Amazon)
Chair (W3C I18N WG)

Internationalization is not a feature.
It is an architecture.

> -----Original Message-----
> From: Ietf-languages [mailto:ietf-languages-bounces at] On
> Behalf Of Doug Ewell
> Sent: Tuesday, July 12, 2016 11:53 AM
> To: Dave Rice <dave at>; Mark_Davis_☕️ <mark at>
> Cc: ietf-languages <ietf-languages at>; Steve Lhomme
> <slhomme at>; draft-lhomme-cellar-matroska at
> Subject: RE: New file format uses ISO 639-2 alpha-3 plus TLDs, ignores BCP 47
> Dave Rice wrote:
> > We had discussion on the cellar list about this but I see that the
> > results of that discussion were used in the EBML draft but did not
> > (yet) impact the current Matroska draft. In our discussion however we
> > were discussing RFC 5646. Is BCP47 preferred?
> BCP 47 is the union of RFC 5646 and RFC 4647. The latter has to do with
> matching of tags, and would probably address some of the questions that
> came up in the January discussion on the cellar list.
> Please feel free to ask us questions about BCP 47 in the course of your work.
> Parts of the January thread definitely indicates a lack of familiarity with BCP
> 47, and reliance on third-party sources (I've tried at least to clean up the
> Wikipedia article).
> --
> Doug Ewell | Thornton, CO, US |
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