This upgrade made org.xwiki.localization.LocaleUtils.isValid() accept locales with a script or extensions (1069 locales instead of 765). Fixed in https://github.com/xwiki/xwiki-platform/pull/6617, which now rejects them explicitly. That rule was decided in https://forum.xwiki.org/t/brainstorming-should-xwiki-support-locales-with-a-script-e-g-zh-hans-sr-latn/18921 (XWiki locales are language[_COUNTRY[_variant]] only).
