Google AdSense allows exporting the data in CSV format, suitable for Microsoft Excel. It doesn't open in Mousepad, Gedit or even in normal spreadsheet programs under Linux. Here's how you can open and use it under Linux.

Open the file in KSpread and choose Unicode ( utf16 ) as its encoding. Also select Tabulator as delimiter in Common tab. That's it.
The bottomline is that you should use utf 16 encoding.