วันไม่เป็นภาษาไทยครับ ผมลองทำดูแล้วมันเป็นภาษาอังกิด

using System.Globalization;
....
....

    protected void Page_Load(object sender, EventArgs e)
    {
        CultureInfo local = CultureInfo.CurrentCulture;
        CultureInfo thCulture = CultureInfo.GetCultureInfo("th-TH");
        CultureInfo enUSCulture = CultureInfo.GetCultureInfo("en-US");
        CultureInfo japCulture = CultureInfo.GetCultureInfo("ja-JP");

        int day = (int)DateTime.Now.DayOfWeek;

        Response.Write ("Local :" + local.DateTimeFormat.DayNames[day] + "<br />");
        Response.Write("Thai : " + thCulture.DateTimeFormat.DayNames[day] + "<br />");
        Response.Write("English - US : " + enUSCulture.DateTimeFormat.DayNames[day] + "<br />");
        Response.Write("Japan : "+ japCulture.DateTimeFormat.DayNames[day] + "<br />");       
    }

Imports System.Globalization

Public Partial Class Default3
	Inherits System.Web.UI.Page
	Protected Sub Page_Load(sender As Object, e As EventArgs)
		Dim local As CultureInfo = CultureInfo.CurrentCulture
		Dim thCulture As CultureInfo = CultureInfo.GetCultureInfo("th-TH")
		Dim enUSCulture As CultureInfo = CultureInfo.GetCultureInfo("en-US")
		Dim japCulture As CultureInfo = CultureInfo.GetCultureInfo("ja-JP")

		Dim day As Integer = CInt(DateTime.Now.DayOfWeek)

		Response.Write("Local :" & local.DateTimeFormat.DayNames(day) & "<br />")
		Response.Write("Thai : " & thCulture.DateTimeFormat.DayNames(day) & "<br />")
		Response.Write("English - US : " & enUSCulture.DateTimeFormat.DayNames(day) & "<br />")
		Response.Write("Japan : " & japCulture.DateTimeFormat.DayNames(day) & "<br />")
	End Sub
End Class

Imports System.Globalization
...
...
...

Protected Sub Page_Load(sender As Object, e As EventArgs)
		
		Dim thCulture As CultureInfo = CultureInfo.GetCultureInfo("th-TH")
		

		Dim day As Integer = CInt(DateTime.Now.DayOfWeek)

		
		Response.Write("Thai : " & thCulture.DateTimeFormat.DayNames(day) & "<br />")
		
	End Sub

IFormatProvider thFormatFromCultureInfo = new System.Globalization.CultureInfo("th-TH", true);
string tempStr = DateTime.Today.ToString("ddd d/MMM/yyyy", thFormatFromCultureInfo);