Наверно эти два массива править:
var headDays = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"];
var headInitial = ["Вс","Пн","Вт","Ср","Чт","Пт","Сб"];
пробуйте заменить на
var headDays = ["Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"];
var headInitial = ["Пн","Вт","Ср","Чт","Пт","Сб","Вс"];