When will any part of ISO 639 list Ulster Scots? I couldn't find it today
in any part. There was certainly a UKMARC code for Ulster Scots, I recall,
but I can't find my UKMARC files at the moment.
Also I mislaid my files of British Library statistics (due to changing
computers a couple of years ago) which listed British Library holdings by
language code, so I don't have the possibility at the moment to identify
the previously used UKMARC code, or the statistics.
Though a new alpha-3 code would be needed now, not the old one.
However, In Ulster Scots, there are now many documents - especially
official ones, as indicated below - as well as many web documents in (and
not just about) Ulster Scots (also known as Ullans) so it definitely fits
the criteria for being used in ISO 639-2.
Given its official status, I propose that it is also suitable for
inclusion in ISO 639-1 as well.
I'm tied up full time in other projects next week, and don't have time to
take the following forward, other than providing this initial information
below, but might one one of the JAC members be in a position to take up
progressing an entry for Ulster Scots in all three parts of ISO 639?
There is a convincing history of use.
There is a longstanding email list (ULLANS-L) and website for Ulster
Scots, and now several more.
Ulster Scots is defined in legislation (The North/South Co-operation
(Implementation Bodies) Northern Ireland Order 1999) as
the variety of the Scots language which has traditionally been used in
parts of Northern Ireland and in Donegal in Ireland 
Furthermore The United Kingdom declares, in accordance with Article 2,
paragraph 1 of the Charter that it recognises that Scots and Ulster Scots
meet the Charter's definition of a regional or minority language for the
purposes of Part II of the Charter 
Relevant links include:
The Ulster-Scots Agency (Tha Boord o Ulstèr-Scotch)
(Language, Identity and Politics in Northern Ireland)
Ulster-Scots voices (BBC site)
Pronunciation of Ulster Scots
Scots Online (http://www.scots-online.org/)
The above information was retrieved from