[PierreProstata]

Holland = Holtland = "wood land", is a/the main region in the Netherlands

Netherlands = Nederlande = "low lands", encompasses the land which is devoid of mountains

Dutch = same origin as Deutsch (like Pennsylvania Dutch, which is closer to German than Dutch)

[rvense]

I've heard that the term Pennsylvania Dutch actually comes from English-speakers mishearing/misunderstanding when the speakers refer to their own language "Deutsch".