The SpreadProcessing library gets into account the current server culture and the SpreadsheetDocumentProvider uses different decimal and list separators based on the culture while the RadSpreadsheet control supports only comma as a list separator and dot as a decimal separator. 

The JavaScript error that is thrown when using the "sv-SE" culture is caused by the fact that this culture uses the comma as a decimal separator and semicolon as a list separator. 

One possible workaround is to change the current thread's culture before creating the Spreadsheet's provider and then restore the culture.