Hi,
If I look at the HTML of the cart module there, I can see both the english and the dutch messages:
monosnap.com/file/KRv6b7ffafJwqF2iQ4lUrOBC2vUktm
And I can also see extra HTML tags and classes that aren't there by default in the HikaShop cart module.
So I suppose that the cart module view has been customized by your template provider with their own translation string (supposing it's not in hard in the view override).
So I'm afraid you'll have to check what to do with your template provider so that they can provide the best method to change that text for different languages.
Ideally, it would be better that they just reuse the text from the option and/or the text from the translation key of HikaShop instead of having their own.