In LuaLibPickle.php, on line 22, the global variable `$wgContLang` is used.
This feature has been completely removed in 1.36.0 (^).
It would be kind to users to warn about that on extension's page.
Topic on Extension talk:Pickle
@Phil.o: It sounds like the compatibility in extension.json should be changed to >= 1.33, <= 1.36 (it accepts any valid Composer version specification).
(Of course, a better fix would be to make it compatible with current versions of MediaWiki! :-) )
Author has left mediawiki a couple of years ago, apparently. And I'm not so confident as to update code to make it compatible with current version.
Github repo has opened issues dating back to 2019. Recent updates are only localizations provided by users, but the core extension seems to be unmaintained.
Module:ScribuntoUnit allows performing unit tests on lua modules, for now.
This extension has some flaws as it stands, and also lacks some core functionality. Development of this version stalled many years ago, but there exist updated code for parts of the extension. It isn't really comparable with any of the existing modules for on-wiki testing, it has more in common with Gherkin, and the updated code have some methods from reasoning.
I'll add a fix for $wgContLang.