BIBFRAME does not require 3 character language codes. URIs are available for ISO 639-1 (2-character codes) and 639-2 (3-character codes). URIs are in the works for ISO 639-3 (a larger list of languages which also encompasses much of 639-2). 

It is neutral on which code list you use. Any examples that show 3-character codes may be transformations from MARC language codes, which are equivalent to the ISO 639-2/B list.
Note that there are a limited number of languages that have 2-character codes; BCP47 ( specifies how to combine the various language code lists.


Rebecca Squire Guenther
Library of Congress
Network Development & MARC Standards Office
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On Jun 30, 2014, at 3:53 PM, Stuart Yeates wrote:

> On 07/01/2014 05:41 AM, Mark K. Ehlert wrote:
>> Stuart Yeates <[log in to unmask] <mailto:[log in to unmask]>>
>> wrote:
>>    My biggest issue (that's not covered in the doc, but which I've
>>    already fed to the doc's authors) is that BIBFRAME mandates
>>    three-letter language codes, where available, while core RDA
>>    mandates two-letter language codes, where available.
> Sorry, there are at least two separate errors in that.
> Correction: Every example I've ever seen using BIBFRAME and language codes uses three-letter codes without any discussion of the interoperability implications with every other thing in the RDF universe that I've seen that uses two letter codes.
> cheers
> stuart
>> To my knowledge, RDA has no such instruction.  There is RDA 7.13.2
>> (Script), where we're told to "expression the language content of the
>> resource using one or more of the terms from ISO 15924..." (mentioned
>> also under 0.12).
>> There's also LC-PCC PS, which points to the MARC language code
>> list for terms rather than codes:
>> <>