3 Answers, 1 is accepted
You can change the tooltips by setting the corresponding localization properties as shown below:
http://demos.telerik.com/aspnet-ajax/window/examples/localization/defaultcs.aspx
Svetlina
the Telerik team

The Localization property was introduced in Q2 2010 release and it seems that your version is older (I did not mention this because you have noted that you are using Q3 2010) - here are the release notes about the version in mention:
http://www.telerik.com/products/aspnet-ajax/whats-new/release-history/q2-2010-version-2010-2-713.aspx
What I can recommend is to upgrade to this build or later and use the properties.
If you, however, prefer not to upgrade you can provide a fake localization by an override as explained below:
http://www.telerik.com/support/kb/aspnet-ajax/window/radwindow-for-asp-net-ajax-localization.aspx
Svetlina
the Telerik team