Please refer to the attached screenshots. A sample project is attached.

There is a known issue in the .NET Framework considering the "fa-IR" culture. Please refer to the following MSDN resource for a solution which is included in the sample project: https://code.msdn.microsoft.com/Fixing-Persian-Locale-for-6e66e044#content

Workaround:

 private void radScheduler1_CellFormatting(object sender, SchedulerCellEventArgs e)
        {
            MonthCellElement monthCellElement = e.CellElement as MonthCellElement;
            if (monthCellElement != null)
            {
                monthCellElement.Header.Text = monthCellElement.Date.ToString("dd", this.radScheduler1.Culture);
            }
        }