Change Box Plot culture and Sumbole

 DataTable table = new DataTable();
        table.Columns.Add(new DataColumn("lower", typeof(int)));
        table.Columns.Add(new DataColumn("q1", typeof(int)));
        table.Columns.Add(new DataColumn("median", typeof(int)));
        table.Columns.Add(new DataColumn("q3", typeof(int)));
        table.Columns.Add(new DataColumn("upper", typeof(int)));
        table.Columns.Add(new DataColumn("mean", typeof(int)));
        table.Columns.Add(new DataColumn("outliers", typeof(decimal[])));

        try
        {
            // calculate age and gender
            List<decimal> arrexp = new List<decimal>();
            int nexp = 0;
            for (int i = 0; i < list.Count; i++)
            {
                arrexp.Add(Convert.ToDecimal(list[i].value));
                nexp++;
            }

            staresults stex = statistics.CalculateBasicStatistics(arrexp.Count(), arrexp.ToArray());
            decimal mean = (decimal)stex.mean;
            decimal median = (decimal)stex.median;
            decimal mode = (decimal)stex.mode;

            //List<decimal> list1 = new List<decimal>();
            var list1 = arrexp.Where(x => x < median);
            var list2 = arrexp.Where(x => x > median);

            staresults q11 = statistics.CalculateBasicStatistics(list1.Count(), list1.ToArray());
            staresults q33 = statistics.CalculateBasicStatistics(list2.Count(), list2.ToArray());
            double q1 = q11.median;
            double q3 = q33.median;
            double upper = (double)arrexp.Max();
            double lower = (double)arrexp.Min();

            ///get the outliers
            double errmax = q3 + (1.5 * (q3 - q1));
            double errmin = q1 - (1.5 * (q3 - q1));

            var errlist = arrexp.Where(x => x >= (decimal)errmax || x <= (decimal)errmin);
            var DatLeftlist = arrexp.Where(x => x < (decimal)errmax && x > (decimal)errmin);

            upper = (double)DatLeftlist.Max();
            lower = (double)DatLeftlist.Min();

            decimal[] errdec = errlist.ToArray();
            table.Rows.Add(new object[] { lower.ToString(), q1.ToString(), median, q3, upper, mean, errdec });

            var boxPlot = BoxPlotChart.PlotArea.Series[0] as BoxPlotSeries;
            if (boxPlot != null)
            {
                boxPlot.OutliersAppearance.BorderAppearance.Color = System.Drawing.Color.Orange;

                boxPlot.ExtremesAppearance.BorderAppearance.Color = System.Drawing.Color.Red;
            }


            BoxPlotChart.DataSource = table;
            BoxPlotChart.DataBind();
        }
        catch
        {
            table.Clear(); 
            BoxPlotChart.DataSource = table;
            BoxPlotChart.DataBind();
        }

  <telerik:RadHtmlChart runat="server" ID="BoxPlotChart" Width="100%" Height="35%">
                                    <PlotArea>
                                        <Series>
                                            <telerik:BoxPlotSeries
                                                DataLowerField="lower"
                                                DataQ1Field="q1"
                                                DataMedianField="median"
                                                DataQ3Field="q3"
                                                DataMeanField="mean"
                                                DataUpperField="upper"
                                                DataOutliersField="outliers">
                                                <TooltipsAppearance Color="White"></TooltipsAppearance>
                                                <Appearance FillStyle-BackgroundColor="#cc66ff"></Appearance>
                                            </telerik:BoxPlotSeries>

                                        </Series>
                                        <XAxis>
                                            <Items>
                                                <telerik:AxisItem LabelText="" />
                                            </Items>

                                        </XAxis>
                                        <YAxis AxisCrossingValue="0" Color="black" MajorTickSize="1" MajorTickType="Outside"
                                            MinorTickType="None" Reversed="false">
                                            <LabelsAppearance DataFormatString="{0:N0}" RotationAngle="0" Skip="0" Step="1"></LabelsAppearance>
                                            <TitleAppearance Position="Center" RotationAngle="0" Text="Expenditure value">
                                            </TitleAppearance>
                                        </YAxis>
                                    </PlotArea>
                                    <ChartTitle Text="Box Plot">
                                        <Appearance Align="Center" BackgroundColor="Transparent" Position="Top">
                                        </Appearance>
                                    </ChartTitle>
                                </telerik:RadHtmlChart>

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            BoxPlotSeries series = (BoxPlotSeries)BoxPlotChart.PlotArea.Series[0]; // Make sure to use your BoxPlotChart's ID
            series.TooltipsAppearance.DataFormatString = "£{0:N2}";
        }
    }