https://meta.wikimedia.org/wiki/Help:Preferences is not up to date.
Also, that page is located on Meta while it should be on Mediawiki.org for consistency concerning documentation.
It is translated manually, outside of the translate extension. Most translations I've checked are clearly outdated.
This task to:
- move the documentation to mw.org
- update the documentation
- mark it for translation
- tell translators about it