The Dutch dictionary is full of nonsense words. For every misspelled word I get a whole list of words that look like a set of rearranged letters that could be Dutch words but aren’t.
I’ve asked Open Taal about it, but they couldn’t be bothered to respond.
Is there a way to edit the standard dictionary?
I’ve only found explanations about edition the custom dictionaries.
LibreOffice uses (mostly) Hunspell dictionaries that are plain text files. Thus, find where they are installed (in your case find the files nl_NL.dic and nl_NL.aff [if it’s Dutch for the Netherlands]) and edit the .dic file. If you want to delete a word, simply delete the respective line. If you want to add a word, you should learn and understand the syntax of paradigms (look into the .aff dile). Note that you should keep the encoding declared in the .aff file, otherwise the dictionary may get corrupt.