I take it your trial license hasn’t expired? If it has, you will not be able to load plug-ins.
What happens when you run the English command with an underscore - i.e. _SetCurrentRenderPlugIn?
I suppose that works if you don’t include the underscore, i.e. just ImpostaPlugInRenderingCorrente.
The underscore forces Rhino to read what follows as a command in English so that you can run it under any language.