I want to change the current week title to two letters, eg: sun to su, mon to mo, in FSCalendar.
You Can Create a Xib and set a label or Button as per Your Requirement.
You can do this by adding a subview in fscalendar for weekDays. I ADDED SINGLE LETTER BUT YOU CAN ADD according to your requirements. 1- create View
Final Step
let week_days_view = weekDaysView.instanceFromNib() as! weekDaysView
week_days_view.frame = self.fsCalendar.calendarWeekdayView.frame
self.fsCalendar.calendarWeekdayView.addSubview(week_days_view)