Added nl-BE locale

[j-dc]

nl-BE uses / as date separator

[Fil]

It would be nice to have a reference. On wikipedia I see

(dd/mm/yyyy)[19] or (dd.mm.yyyy)[20][21]

but no mention of which is the most common occurrence.

[j-dc]

I could change wikipedia for you... ;-) ;-) But the following code is how browsers do it. I hope this is enough of a reference for you?

The dd.mm.yyyy format is indeed accepted in this country, but it feels like something my grandfather used..

var date = new Date();
console.log(new Intl.DateTimeFormat('nl-NL').format(date));
console.log(new Intl.DateTimeFormat('nl-BE').format(date));

Output:
24-11-2021
24/11/2021

https://jsfiddle.net/gw9Ltho8/