Could we have $wgCategoryCollation set to uca-default for gdwiki, please.
This has been discussed by the community with clear consensus in favour, 9-0:
Further information: Even if a collation uca-gd exists (and I am not sure whether it does), uca-default is perfectly adequate and suitable for Scottish Gaelic, which has no unusual sorting requirements, just a few accented characters similar to Italian. I understand that the conversion to uca has in the past run into technical problems and run very slowly for very large Wikipedias (e.g. French) while it has gone smoothly for smaller Wikipedias. The Scottish Gaelic Wikipedia is small with less than 14,000 articles.