First:I use EditFile.aspx to edit SiteFooter.ascx. I click Save_Click Button to save SiteFooter.ascx after add chinese words.
Second:Footer of web display chaos encoding when I visit web

Does the browser have all the right language packs, and what was your specific error?

My answer:
EditFile.aspx.cs:
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.IO;


namespace Wrox.WebModules.FileManager.Web
{
   public class EditFile : System.Web.UI.Page
   {
      protected System.Web.UI.WebControls.Label StatusMessage;
      protected System.Web.UI.WebControls.TextBox SaveAsPath;
      protected System.Web.UI.WebControls.TextBox FileContent;
      protected System.Web.UI.WebControls.Button Save;
      protected System.Web.UI.WebControls.Table Table1;
      protected System.Web.UI.WebControls.Button Back;

      private void Page_Load(object sender, EventArgs e)
      {
         if (!IsPostBack)
         {
            string filePath = Request.Params["File"];
            if (filePath != null)
            {
               if (Request.Params["CreateFile"] == null || Request.Params["CreateFile"]=="false")
               {

                  try
                  {
                     StreamReader sr = new StreamReader (File.Open(Server.MapPath(filePath), FileMode.Open),System.Text.Encoding.GetEncoding("g b2312"));
                     FileContent.Text = sr.ReadToEnd();
                     sr.Close();
                  }
                  catch (Exception exc)
                  {
                     StatusMessage.Text = exc.Message;
                     StatusMessage.Visible = true;
                  }
               }
               SaveAsPath.Text = filePath;
            }
         }
      }

      protected void Back_Click(object sender, EventArgs e)
      {
         string filePath = Request.Params["File"];
         if (filePath != null && filePath != "/")
         {
            int lastSlashIndex = filePath.LastIndexOf("/");
            string folderPath = filePath.Substring(0, lastSlashIndex+1);
            Response.Redirect("BrowseFiles.aspx?Folder=" + folderPath);
         }
         else
            Response.Redirect("BrowseFiles.aspx");
      }

      protected void Save_Click(object sender, EventArgs e)
      {
         try
         {
            string filePath = SaveAsPath.Text;
            if (!filePath.StartsWith("/")) filePath = "/" + filePath;
            StreamWriter sw = new StreamWriter(Server.MapPath(filePath),false,System .Text.Encoding.GetEncoding("gb2312"));
            sw.Write(FileContent.Text);
            sw.Close();
            StatusMessage.Text = "Îļþ³É¹¦±£´æ";
         }
         catch (Exception exc)
         {
            StatusMessage.Text = exc.Message;;
         }
         StatusMessage.Visible = true;
      }


      #region Web Form Designer generated code
      override protected void OnInit(EventArgs e)
      {

         base.OnInit(e);
         InitializeComponent();
      }

      private void InitializeComponent()
      {
         this.Load += new System.EventHandler(this.Page_Load);

      }
      #endregion
   }
}