Dates on [[ku:Special:Notifications]]
Yeah, I did. Those are all translated. I found EDTF, maybe it has something to do with those?
According to your screenshot, these dates do not seem to be generated from MediaWiki messages, but from other internal libraries (part of PHP itself, or inside its own C/C++ dependencies?). If so, they are likely maintained in CLDR and imported later in those libraries, or integrated manually in those libraries. I have never seen these dates untranslated in languages I use. You may need to submit your question and screenshot in Phabricator, to know where they come, or if there's a need to modify the PHP code to support additional translations (e.g. if the PHP code just uses some PHP date formating function, such as those documented in the https://www.php.net/manual/en/datetime.formats.date.php extension or in https://www.php.net/manual/en/intldateformatter.format). I may be wrong, but EDTF was created much more recently than MediaWiki and PHP, and is unlikely to be used for those notifications and used as a dependency in MediaWiki.