Resources folder in the package contains the copies of resource files such as the language files which are already embedded into GleamTech.FileUltimate.dll. For example, you can use these files to create a new translation or modify an existing translation. You should copy the modified files to the corresponding place under Project\App_GlobalResources to override an embedded resource. Please only copy the required files and not the whole folder as future updates to GleamTech.FileUltimate.dll may include newer versions of those files which may be necessary to run the latest version properly.
New or modified files under Project\App_GlobalResources folder should trigger restarting of the ASP.NET application. So, FileUltimate should automatically recognize the changes to the resource files under this folder. If FileUltimate does not recognize the changes then you can touch (simply open & save) Project\Web.config file to force FileUltimate to see the changes.
Please see the below article for information on translating FileUltimate: