Néerlandais vs. hollandais
The French words 'néerlandais' and 'hollandais' both refer to Dutch, but they have subtle differences in usage and scope.
Néerlandais
'Néerlandais' is the more comprehensive and officially correct term for the Dutch language and people from the Netherlands.
Je parle néerlandais.
(I speak Dutch.)
Les Néerlandais aiment faire du vélo.
(The Dutch like to cycle.)
La littérature néerlandaise est fascinante.
(Dutch literature is fascinating.)
Hollandais
'Hollandais' technically refers specifically to people or things from the provinces of North and South Holland, but is often used informally to mean Dutch in general.
Le fromage hollandais est délicieux.
(Dutch cheese is delicious.)
Amsterdam est une ville hollandaise.
(Amsterdam is a Dutch city.)
La sauce hollandaise est populaire en cuisine.
(Hollandaise sauce is popular in cooking.)
Summary
While 'néerlandais' is the correct and inclusive term for all things Dutch, 'hollandais' is often used colloquially but technically refers to just Holland. 'Néerlandais' is preferred in formal contexts, while 'hollandais' is common in everyday speech and certain traditional phrases.