Since this is just a panel that's available on-demand anyway, perhaps
having an additional dropdown switch to select English/canonical vs.
project-local namespaces/keywords would be handy if it can be made not
too clutter-y.
These kind of choices seem more natural for me to be made when using the data rather than when it is collected. That is: I copy a code that can be used anywhere ("File"), when I paste it into a German wikipedia it either: (a) gets adapted automatically, (b) gets adapted and provides a choice to undo the automatic adaptation or (c) is not modified but an option is provided to do so.
This is how copy&paste works in many places with respect to paste with format, or in plain text. Putting those decisions upfront seems like unnecessary cognitive load.
Pau