As a foreign researcher coming to the Netherlands, you will probably work in an entirely English speaking environment. However, this does not mean that you do not need to learn Dutch. Even though you might interact primarily with other internationals on a professional level, knowledge of the Dutch language is essential in daily life. When it comes to filling in official forms and documents (e.g. for housing, banking, insurance schemes and social activities) English will probably not get you very far. A wide range of Dutch language courses is available, some cheap and expensive, some lasting from a few weeks to several years.
A complete list of the language courses available in Amsterdam can be found via the link below.