Ajaxリクエスト時に中国語が文字化けして送信される問題の解決方法

function UpdateFolderInfoByCustId(folderId, folderName, custId) {
$.ajax({
type: "Post",
contentType: "application/x-www-form-urlencoded; charset=utf-8",
url: "http://localhost/CRM/Ashx/HandKBSucessCustomer.ashx?Method=UpdateCustomerByCustId&folderId=" 
+ folderId + "&folderName=" + encodeURI(encodeURI(folderName)) + "&custId=" + custId,
success: function (msg) {
alert(msg);
},
error: function (error) {
alert(error);
}
});
}

public void UpdateCustomerByCustId()
{
int folderId = Convert.ToInt32(Request["folderId"]);
string folderName = Request["folderName"];
string folderName2 = Convert.ToString(System.Web.HttpUtility.UrlDecode(folderName));
int custId = Convert.ToInt32(Request["custId"]);
bool res = false;
try
{
res = CustomerBusiness.UpdateCustomerByCustId(folderId, folderName2, custId);
}
catch (Exception ex)
{
throw;
}
Response.Write(res);
}
}
}