There is a open source project on codeplex that tries to add the missing RTL functionality in Silverlight 2:
Unfortunately RadControls for Silverlight do not support RTL out of the box. Generally speaking, all we have to do is to replace all ContentPresenter and ContentControl controls in all RadControls' templates with the special ContentControl from the link above. However, this might not work seamlessly with all controls and might require some coding on our side. I cannot promise such support for the upcoming service pack next week, but we could try to provide a custom theme which has RTL support with the Q2 release, which is scheduled for the summer.
We will be glad to help if you try to create such theme, so please, do not hesitate to write again with any problem you might encounter.
the Telerik team
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