When creating a multilingual form via the sharepoint menu (New->Forms for Excel) or from within an excel file in Sharepoint, the language column does not appear in the underlying (connected) Excel file.
However I did find a workaround. If you Sync all responses to a new workbook, the language column now appears in the new file !
NOTE : This issue is not experienced if you create the Forms via Forms and the excel file is 'disconnected'.
