HowTo send JSON data from WCF service with special characters

The manner to return special characters within the JSON response of a (SharePoint-based) WCF REST service, consists of 3 essential elements:

1. Define the method response as System.IO.Stream;
2. Set the charset of the JSON response to 'ISO-8859-1';
3. Apply UniCode encoding to the JSON response string.

Code example

 [ServiceContract(Namespace = "...")]
 public interface IRESTService
 {
    [WebInvoke(Method = "GET", 
     UriTemplate = "/RESTMethod?$parameter1={parameter1}&...",
     RequestFormat = WebMessageFormat.Json,
     ResponseFormat = WebMessageFormat.Json,
     BodyStyle = WebMessageBodyStyle.Bare)]
    System.IO.Stream RESTMethod(string parameter1, ...);
}

[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Required)]
public class RESTService : IRESTService
{
   public Stream RESTMethod(string parameter1, …)
   {
       OutgoingWebResponseContext context = 
          WebOperationContext.Current.OutgoingResponse;
       context.ContentType = "application/json; charset=ISO-8859-1";
  
       string jsonData = ...;
       return new MemoryStream(UnicodeEncoding.Default.GetBytes(jsonData));
   }
}