Per this RfC on meta, we should change the default for $wgCategoryCollation from "uppercase" to "uca-default-u-kn". For now, Wiktionary projects should be exempted (and remain "uppercase") if possible. Also, any languages that have customized versions of icu, for example, uca-fr-u-kn, should be switched to that in the process. See https://www.mediawiki.org/wiki/Manual:$wgCategoryCollation#Language-specific_collations.
Once this is complete, we should run updateCollation.php on all the affected wikis.