The CS department at the German university I work for started offering their lectures in English a number of years back. While a very good command of English is not uncommon in other parts of Europe, such as e.g. Scandinavia, this move is remarkable in my opinion because English is (more or less) ubiquitous only in the younger generation in Germany. A lot of middle-aged people do not speak English, or only at a very…
Not speaking Dutch is all fine while you’re on your student visum in an English speaking environment, but it breaks down when you have to pay taxes or get a letter from the immigration office—all that is in Dutch.
Personally, I think it is great to learn a new language, and you’ll gain a lot from it as a person, but there is also a real necessity to it once you start to live somewhere for a longer time—a fact that one might not immediately recognise because of European enthousiasm to speak and interact in English.