not all patterns are automatically available in all languages.It always depends on whether the individual author of that pattern is able to provide it in several languages - there's no computer translating it automatically.
Generally, a good indicator is the language of the description text itself - if that is in Dutch, then the pattern should be as well. If not, then chances are the pattern isn't either. Please contact the author of the pattern and ask for a translation into Dutch.
You can write a message by clicking on the contact button in the author's store.