I recently got curious about the roots of this, and it turns out it’s from Celtic languages. All the Celtic languages count in base 20, and they were widespread

I recently got curious about the roots of this, and it turns out it’s from Celtic languages. All the Celtic languages count in base 20, and they were widespread across continental Europe before the Romans introduced Latin to their conquests and then the Germanic tribes brought the Germanic languages in. Celtic remained a strong influence around modern France, Belgium, the Netherlands so we end up with French counting partially in 20s, even though continental Celtic languages are extinct (Breton, spoken in north west France is an insular Celtic language, more closely related to Celtic as spoken in the British isles and Ireland.) I don’t know how Danish got base 20 counting though. Must have more reading to do.