The JS file with the stringResources shipped with the installation at the following location:

C:\Program Files (x86)\Progress\Telerik Reporting <Release>\Html5\ReportViewer\js

is incorrect, it should be as shown in the Localization - Telerik Reporting article.

Basically, line 9 should be changed to:

; (function (trv, $) {

while lines 178 to 180 should be like this:

    trv.sr = $.extend(trv.sr, sr);

}(window.telerikReportViewer = window.telerikReportViewer || {}, jQuery));