To allow localization for the WebReportViewer in Version 17.1.23.718 and before, it was enough to provide a customized Version of "telerikReportViewer.stringResources.js", which extended the property "window.telerikReportViewer.sr".

This worked for both, the WebReportViewer and the Preview of the WebReportDesigner. With version R3 2023 SP1 (17.2.23.1114), this approach does not work anymore.