The Swedish locale is defined like this:
DayPilot.Locale.register(new DayPilot.Locale('sv-se',
{
'dayNames':['söndag','måndag','tisdag','onsdag','torsdag','fredag','lördag'],'dayNamesShort':['sö','må','ti','on','to','fr','lö'],
'monthNames':['januari','februari','mars','april','maj','juni','juli','augusti','september','oktober','november','december',''],
'monthNamesShort':['jan','feb','mar','apr','maj','jun','jul','aug','sep','okt','nov','dec',''],
'timePattern':'HH:mm',
'datePattern':'yyyy-MM-dd',
'dateTimePattern':'yyyy-MM-dd HH:mm',
'timeFormat':'Clock24Hours',
'weekStarts':1
}));
It looks like the locale might not be set correctly (using the default "en-us" locale?).
Running this following code in the JS console at the calendar demo page seems to work:
dp.locale = "sv-se";
dp.update();
http://javascript.daypilot.org/demo/calendar/index.html