As a foreign researcher in the Netherlands you will probably work in an entirely English speaking environment. Although you will interact primarily with other internationals, 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. Secondly, it is likely that your Dutch colleagues and neighbours will appreciate it if you make the effort to speak Dutch.
There is a wide range of Dutch courses available. The courses vary in duration, frequency and price. Your employer may even offer you free or reduced-rate Dutch courses in-house. It is worthwhile asking your employer about the options available.