The up-to-date resource files for all controls (App_GlobalResources folder) is distributed with each Telerik UI for ASP.NET AJAX release. You can find them either into the controls installation folder, e.g.:
C:\Program Files (x86)\Telerik\UI for ASP.NET AJAX Q1 2015\App_GlobalResources
or in the controls archive, downloaded from a client's Telerik account.