These characters show fine when I cut-and-paste them here from the VisualStudio debugger, but both in the debugger, and in the TextBox where I am trying to display this text
I was facing similar problem.
It was problem with reading file properly and not with TextBox control.
TextBox
StreamReader reader = new StreamReader(inputFilePath, Encoding.Default, true)
Copied from THIS.
Works for me and that too without switching to RichTextBox.
RichTextBox