Change the text in date field label (YYYY)

Hi,

Quick question: ive managed to change the text in adress fields (to Dutch) using this piece of code:

// Label: Gravity Postcode
add_filter("gform_address_zip", "set_gravityform_address_zip");
function set_gravityform_address_zip($label){
return "Postcode";
}

How can i use this to change the text in the labels for the 'date field'?

I want to change YYYY to JJJJ (the dutch word for year = jaar)

Thanks :-)