Hi Bash,
You simply need to paste following JSON in DatePicker's AdvancedFormat -> AdvancedFormatJSON property as shown in screenshot.
JSON
"{
i18n : {
previousMonth : 'Vorige Maand',
nextMonth : 'Volgende Maand',
months : ['Januari','Februari','Maart','April','Mei','Juni','Juli','Augustus','September','Oktober','November','December'],
weekdays : ['Zondag','Maandag','Dinsdag','Woensdag','Donderdag','Vrijdag','Zaterdag'],
weekdaysShort : ['Zo','Ma','Di','Wo','Do','Vr','Zat'],
todayButton : 'Vandaag'
}
}"

Hope it helps, Thanks :)