Changing the language of AJAX Control Toolkit Calender Extender Control

If you are using Ajax control tool kit then you have a Script manager on your aspx file, and it probably looks like this

asp:ScriptManager ID="ScriptManager1" runat="server"

Well, this will let you work with Ajax controls.However your calender extender's language will probably be English.If you need to change calender extender's culture what you need to do is below
Step 1: Check if you between your <@ Page /> tag you have set Culture as you wish it to be such as Culture="tr-TR"
Step 2: Add EnableScriptGlobalization to your script manager, and set it True then you will have

asp:ScriptManager ID="ScriptManager1" runat="server" EnableScriptGlobalization="true"

This will probably work, you can also check for another ways to do this on How to change the Culture of CalendarExtender programmatically.