The official language of the Netherlands is Dutch, but most people speak English as well. Many of them also speak German and French. As a result of international trade, centuries of immigration and historical ties with the rest of the world he Dutch are keen to learn foreign languages. Learning Dutch before coming here is not necessary, but the Dutch appreciate it when you try to master the basics of their language.
The Netherlands was the first non-English speaking country to offer degree programmes taught in English. The country is ahead of the rest of continental Europe in this respect. It is also the largest non-English speaking importer of English books, so buying books in Groningen won’t be a problem at all.