When you have localization turned on, and you are an administrator (i.e. your current role is the same as that defined in the behavior setting named ADMIN_OVERRIDE_ROLE), then there will be an additional prompt at the top of the Custom Report, the Summary Report and the Chart screens, when you are editing the report and as shown below:
Localizing a Report Description
The Localize button can be used to provide a localized description of the report for each locale you have defined. However, note that you cannot localize the Report Title. The reason for this is that each Report Title must be unique through the entire system.