Continuing with this old thread:
It looks like that the CLDR has changed its mind and nowadays the first weekday for Ireland is officially Monday and not Sunday as you can check in the CLDR's supplementalData.xml:
Would it be now possible to apply the patch proposed by Daniil Zhilin?
This looks reasonable, see also: https://unicode-org.atlassian.net/browse/CLDR-11192
Thank you for filing this issue. As CLDR provides the supplemental data per territory rather than per locale, I think the same change should be made to ga_IE as well. Please find the patch amended and reposted here:
The master branch has been updated by Rafal Luzynski <email@example.com>:
Author: Daniil Zhilin <firstname.lastname@example.org>
Date: Sun Nov 27 22:46:26 2016 +0300
ga_IE and en_IE locales: Revert first_weekday removal (bug 24200).
These values were removed by the commit 0a410e76f5.
* localedata/locales/ga_IE (first_weekday): Add, set to 2 (Monday).
* localedata/locales/en_IE (first_weekday): Likewise.
This bug has been fixed in master. Thank you Daniil and Alberto for your contributions.