You need to have the ReportViewer Language Pack (this is probably the version you need Microsoft Report Viewer Redistributable 2010 Language Pack).
Also have a look at How to localize the ReportViewer control in ASP.NET 2.0 as it provides more information of localizing the report viewer.
Perhaps this article can also help you: Customizing and Localizing Microsoft ReportViewer .NET - An exact solution.