I want to use Telerik Silverlight controls in one of my project in which I want to have Arabic User Interface. Can you please tell me whether Telerik Silverlight Control supports Arabic Language?
Yes, the RadControls for Silverlight suite has support for localization through the LocalizationManager. If you go to this link, you will learn how to enable localization support in your application. As long as you've properly set your application up to leverage the localization features of .NET and you've enabled the localization features of RadControls, you shouldn't have any problems.
Also, along with the overview of localization of the entire Silverlight components, some individual controls will have it's own section on localization. For example, here are links to the documentation on localization of the RadScheduleView, RadRichTextBox, RadGridView and RadDocking controls.
While searching on RTL Support on Telerik Controls I found that some Telerik Controls not supported RTL.
I want to know about whether all Telerik Silverlight Controls supported RTL? If not can you please provide me a list of Telerik Silverlight controls which supports RTL.
You're looking for the "FlowDirection" attribute. If you set FlowDirection="RightToLeft", you can explicitly set the direction the text. As I said in the previous post, you can utilize the LocalizationManager to properly set all of the RadControls. However in some circumstances, like a RadRichTextBox, you'll want to add additional parameters.
I've prepared a Google search for you to help you dig deeper. This link will load targeted search results about using RTL. For future searches, use the search term "RightToLeft" instead of "RTL", this is because the property name will return more hits than the abbreviation.