dict file

One possibility is to download the free Dictionaries for Mac application, and add the Nederlands English <-> Dutch dictionary which is installed into the Apple Dictionary application list of dictionaries. It is preselected, so it will appear as an option to the right >> of the dictionary toolbar. A lifetime license for the dictionary and its updates is $20.

When you launch the Dictionaries for Mac App, it will have an Add Dictionary button. Click that and scroll down among the dictionaries to Nederlands Dutch entry. Otherwise, contact the vendor for support.