In your document, press ALT+F9 to display field codes. You should be able to see your STYLEREF now. Replace it with this one. Remember, create the pairs of braces using Ctrl+F9. When done, press ALT+F9 again.

Since I don't have access to another language, I can't create a Kop 1 in my doc, but I did test that I get my Heading 1 text if the word English is in the Category property, and if it isn't, then I get the standard error that it can't find style Kop 1.