Automatically switching to rtl direction on selecting Arabic language is a tough one, though - you can create two separate themes for your site in two theme folders in the App_Themes
directory of your project. You can find more information on how to create and register a backend theme on this section
of our Designer's Guide. One of the themes will be used by your English pages. When you create an English page you will select the page to use that theme. In the second theme you will style your CSS so that the text direction is right to left, and you will set your Arabic pages to use this theme.
Another option is to hook to the index changed event of the language dropdown list in the administration - it is a standard Asp.Net control, and check which is the selected item's value. Then you can include a CSS style dynamically, based on that value.
You can also switch, let's say two CSS files depending on the language selected. This might happen in the Page_Load event.
All the best,
the Telerik team
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