Context. There isn’t a specific term for the grouping of the three countries in either language that I know of.The Low Countries are Netherlands, Belgium and Luxembourg. How do Spanish- and French-speakers make it clear that when they say "Paises Bajos" or "Pays-Bas," they're referring only to Holland?
Considering the defeats that both Spain and France had in that region, maybe they don’t want a special term for it.
It’s hard enough as it is to get French-speaking Belgians and Dutch*-speaking Belgians to agree that they’re a part of the same country.
* - OK, Flemish, but it’s really Dutch.
