The issue is not reproducible with Telerik Reporting Q1 2016 SP1 v10.0.16.211, and a report witth TextBox item with Culture set to 'ar'. The report displays the text in the same way in design preview, PDF and HTML (the HTML5 Viewer).
Please check if you are using a TextBox item and setting its Culture property resolves the issue. Also check if the above mentioned version of Telerik Reporting changes the way the content is rendered. External CSS rules may also affect the rendered HTML, thus inspect the HTML with the browser's developer tools and trace the style inheritance.
In order to provide you more accurate suggestions, please provide step by step instructions how to reproduce the problem, or open a support ticket and send us a demo report.
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