Generic solution for encoding when writing to a file

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C#

WinForms

Hi all,
I have a method that export data to a file(.txt or .csv). all works fine except the encoding.

the exported data contains caracters such as (é, à,...), those caractere appears incorrectly in same computers while it works fine in others.

here is the code.

using (StreamWriter sWriter = new StreamWriter(stream, Encoding.UTF8))
{
   sWriter.WriteLine("Nom ; Prénom ; Adresse ; Code postal ; Ville ; Prospection ; Fixe1 ; Fixe2 ; Fax ; Portable");

   foreach (ExtendedContact c in extendedContactList)
   {
      if (cb_prospection.Checked)
      {
         if (c.Prospection != "Contre")
         {
            sWriter.Write(OneSpace(c.Nom) + ";" + OneSpace(c.Prenom) + ";" + OneSpace(c.Address) + ";" + OneSpace(c.CodePostal) + ";" + OneSpace(c.Ville) + ";" + OneSpace(c.Prospection) + ";" + OneSpace(c.Fixe1) + ";" + OneSpace(c.Fixe2) + ";" + OneSpace(c.Fax) + ";" + OneSpace(c.Portable));
            sWriter.WriteLine();
         }
      }
   }
}

I want to create a generic solution that works in any computer.
what do you think is the best solution? do i have to give the user to select between diffrent kind of encoding(i am totaly aginst since many user don't know what encoding is)?

Thanks