@msc.bs
To translate email headers to another language (e.g. French) please use following code example.
MailMessage msg = new MailMessage("from@host.com", "to@host.com", "subject", "body")
msg.Date = new DateTime(2015, 1, 1, 18, 29, 59);
HtmlSaveOptions htmlSaveOptions = new HtmlSaveOptions();
htmlSaveOptions.HtmlFormatOptions = HtmlFormatOptions.WriteHeader | HtmlFormatOptions.DisplayAsOutlook;
msg.Save(@"d:\test_en.html", htmlSaveOptions);//english
CultureInfo culture = new CultureInfo("fr-FR");
htmlSaveOptions.FormatTemplates[MhtTemplateName.DateTime] = String.Concat(culture.DateTimeFormat.LongDatePattern, " ", culture.DateTimeFormat.ShortTimePattern);
htmlSaveOptions.FormatTemplates[MhtTemplateName.From] = htmlSaveOptions.FormatTemplates[MhtTemplateName.From].Replace("From:", "De :");
htmlSaveOptions.FormatTemplates[MhtTemplateName.Sent] = htmlSaveOptions.FormatTemplates[MhtTemplateName.Sent].Replace("Sent:", "Envoyé :");
htmlSaveOptions.FormatTemplates[MhtTemplateName.To] = htmlSaveOptions.FormatTemplates[MhtTemplateName.To].Replace("To:", "À :");
htmlSaveOptions.FormatTemplates[MhtTemplateName.Cc] = htmlSaveOptions.FormatTemplates[MhtTemplateName.Cc].Replace("Cc:", "Copie :");
htmlSaveOptions.FormatTemplates[MhtTemplateName.Subject] = htmlSaveOptions.FormatTemplates[MhtTemplateName.Subject].Replace("Subject:", "Objet :");
msg.Save(@"d:\test_fr.html", htmlSaveOptions);//french