You can do a few things here.
1. On the dropdown list you can set the auto post back property to true and assign an event handler to it. This will cause the form to refresh every time a selected value changes. Then have an event handler for SelectedIndexChanged and inside the event handler update your page accordingly.
Here is the mark up and C# codebehind
<asp:dropdownlist runat="server" id="foo" autopostback="true" onselectedindexchanged="foo_SelectedIndexChanged" xmlns:asp="#unknown"></asp:dropdownlist>
protected void foo_SelectedIndexChanged(Object sender, EventArgs e){
}
2. If you absolutely must redirect using Response.Redirect then you can add a parameter to your response like this MyStuff/Languages/Alphabets.aspx?dropdownvalue=myvalue and when the form loads again you can read the value like this Page.Request.QueryString["dropdownvalue"]. Once you read the value simply set the value of the drop down.
Trigger page reload
Response.Redirect("~/MyStuff/Languages/Alphabets.aspx?dropdownvalue=myvalue");
Handle reload response
protected void Page_Load(object sender, EventArgs e)
{
string dropdownvalue = Page.Request.QueryString["dropdownvalue"];
}