Hello calm_boy,
Please check this article on how to achieve that:
http://www.telerik.com/help/aspnet-ajax/localizing-radupload.html
Note, that you need to have at least the Q2 2008 version of RadControls.
Sincerely yours,
Veselin Vasilev
the Telerik team
Check out
Telerik Trainer, the state of the art learning tool for Telerik products.