Superlatives with location

Question

Why is it "la plus parlée *au* monde"? The relevant lesson says to use "de": https://progress.lawlessfrench.com/revision/grammar/how-to-form-the-superlative-of-adjectives-in-complex-cases

Accepted Answer

Bonjour Adrian,
Chris is right! It is far more common to use "au monde" (or "dans le monde") than to use "du monde" with superlatives. We've now accepted "du monde" although in this particular instance (i.e. with the word "langue"), it sounds a little strange.
I hope this is helpful.
Bonne journée !

Answer

Actually, I think du monde would also be OK to use, even though I gravitate more towards au monde, as the most frequently used form.In English, you could also say, "in the world" even though "of the world" is probably more common.