C# Convert console output UTF-8 to display in textbox - special characters problems

Hello,

I do a project on C#.

I lunch a process in my source code, especially a console command.

startinfo.redirectstandartoutput and input are activated.

I redirect the output in UTF-8 with this line : StartInfo.StandardOutputEncoding = UnicodeEncoding.UTF8;

And then is a problem, I wan't to write the output of the process  on a textbox (or a richtextbox), but the french 'é' or 'è', I mean the french special caracters aren't correctly passing (correctly write on the console, but no after the output).

What can I do to write a console standartoutput with 'é' or 'è' correctly on my textbox (or some other) ?

Thank you on the peoples who can help me.