Which word did you add? Did you verify that it is your personal dictionary? Also, if a word is in the dictionary with a capital, it only verifies with a capital.

Example: "De windmolen heeft wieken van hoekprofiel." Both words 'windmolen' and 'hoekprofiel' give a spellcheck error. If I right-click on the word I get a pop-up with an "Add to dictionary" option. I choose this option but this has no effect. A lot of Dutch word combinations are written as one word without a 'space' in between. Like 'wind' and 'molen' . "glove compartment" is "handschoenkastje" in Dutch. One word. This gives a spelling error. I'm not sure if I use my personal dictionary.(?) I assumed I added words to the selected (Dutch) dictionary.

Words you add don't get added to the selected dictionary, but to your own personal dictionary. I don't think this personal dictionary is specific for the language you are using, so if you add a word there, it will be recognized for every language you do spell checking.

I think you have to start spell checking all over after you have added new words, in order to recognize the new words.

And I'd say that 'glove compartment' is 'handschoenenkastje' in Dutch (plural, because it can contain more than one glove) :-)