Hi,

You will have to handle this on your own in the begin request event in the CMSAppBase.cs file. You will check what URL/document is requested, what is the culture in current context and decide whether you will combine it with default culture or not.

As your question concerns adding complex functionality to Kentico and would require very in-depth explanations, I would recommend that you consider our paid consulting services which would offer you much more detailed and hands-on support for this project. You can find more information here:

http://www.kentico.com/Support/Consulting/Overview

Your question is particularly well suited for the consulting service. Keep in mind if you do have any specific questions regarding use of the API or you encounter any errors or general issues during your development, you can contact support as usual.