public static int GetWeekOfYear(DateTime dt)
{
    CultureInfo myCI = new CultureInfo("zh-CN");
    Calendar myCal = myCI.Calendar;
    CalendarWeekRule myCWR = myCI.DateTimeFormat.CalendarWeekRule;
    DayOfWeek myFirstDOW = myCI.DateTimeFormat.FirstDayOfWeek;
    return myCal.GetWeekOfYear(dt, myCWR, myFirstDOW);
}

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C# code
using System.Globalization;