To preview/export localized reports in different languages, I change the thread's current culture in the report viewer's ExportBegin/RenderingBegin events and reset it back to the original culture in the ExportEnd/RenderingEnd events.
This approach works well in .NET Framework projects but in .NET Core projects, the culture is not reset properly.
Changing the culture in the events of the desktop report viewers should work both in .NET Framework and .NET Core projects.