That exception makes sense. Both because their prescription isn’t in the dictionary itself, but rather in their choice of scope for it, and because it’s trying to protect a threatened variety, instead of just creating some meaningless division (like plenty prescriptions do).
variety
Language! High German may have an army but we have the fleet.
More seriously if you class Low Saxon as a non-standard variety of Standard German and then have a look at the family tree you’d have, for the sake of consistency, call English a German variety. Sure they’re all West Germanic languages but we need taxa for the taxonomy god: Low Saxon is more closely related to the Anglo-Frisian languages than to the Allemannic/Bavarian line, which is where Standard German stems from.
