Toki Pona is a constructed language without a standard language code. There used to be a Wikipedia in it, so MediaWiki supports localization into by having a json localization file in core and some extensions. However, the Wikipedia is closed (and moved to Wikia), and translatewiki doesn't support localization into it.
Since the code is non-standard and wider activity is not expected, the code and the json files should be removed. It would be nice to give the maintainers of the Wikia site a way to keep the localization, however.
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Copying/adapting the (incomplete?) to-do list from merged task (T178730#3701525):
[] Toki Pona localization files be removed from MediaWiki,
[] the ability to add descriptions in Toki Pona be removed from Wikidata,
[] remove localizations from Translatewiki
[] Update the [[https://translatewiki.net/wiki/Portal:Tokipona |Tokipona portal]] to reflect this new status