This will help in #11130 (cc @sprintr).
It defines all preferences we have in core.
Define all preferences in core
@MarcelGerber This looks fine to me. We can get this in so I can remove them from data.json and add descriptions to them.
can we remove data.json after this is merged? (part of #11200 )
We only need language and path from data.json since they are not prefs but layers of the preferences system. We can hardcode them in main.js