https://www.sussex.ac.uk/informatics/punctuation/apostrophe/...
In dutch, nouns that end in the single vowels '–a', '-i', '-o', '-u', '-y' get a "-'s" when forming the plural. The apostrophe is added to keep the long single vowel at the end long.
That's why dutch speakers frequently make this mistake.
https://www.sussex.ac.uk/informatics/punctuation/apostrophe/...