In https://github.com/wikimedia/language-data/pull/37 , there was a major update to language codes. It is supposed to make the language codes usage more standard, and it is known to fix some known bugs, but it may also introduce some issues, and shouldn't be merged and deployed without thorough testing. It may affect Wikidata and other components that use language-data.

Creating this task to plan this testing and to mark the other affected issues.

The Gerrit patch is https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/UniversalLanguageSelector/+/491213/