Account creation on https://foundation.wikimedia.org/ is disallowed on purpose. That's a choice, but a side effect of that decision is that Special:Preferences isn't available. And while translations like https://foundation.wikimedia.org/wiki/Naming_Convention_Proposals_Movement_Feedback_Survey_Privacy_Statement/de do exist, the interface language can't be changed other than with uselang. The UniversalLanguageSelector is available, but nothing can be configured without logging in.
Other settings that a user may want to change despite not editing:
- Use another skin, there's no way but to use useskin.
- Gender (but it may not be widely used on foundationwiki)
- Thumbnail size
- Disable mediaviewer
- Math appearance (don't know if foundationwiki uses it at all)
- Search settings
- Gadgets (ExLinks, Wiktionary Hover, Navigation popups, Reference Tooltips and CurIDLink) may be desired despite not editing the wiki
It would be desirable to be able to configure these settings. Language could perhaps be done with ULS and cookies.