You have a downloaded text file in UTF-8 format. You must you have read the file to get that string. So why not set the encoding when you read it and let reader do the conversion?
TextBox1.Font = New System.Drawing.Font("DejaVu Sans Mono", 10, _
System.Drawing.FontStyle.Regular, _
System.Drawing.GraphicsUnit.Point)
Dim fs As IO.FileStream = IO.File.OpenRead(Utf8_FilePath)
Dim sr As New IO.StreamReader(fs, System.Text.Encoding.UTF8)
While sr.Peek <> -1
TextBox1.AppendText(sr.ReadLine() & vbCrLf)
End While
sr.Close()
Even less code:
TextBox1.Font = New System.Drawing.Font("DejaVu Sans Mono", 10, _
System.Drawing.FontStyle.Regular, _
System.Drawing.GraphicsUnit.Point)
Dim sr As IO.StreamReader = IO.File.OpenText(Utf8_FilePath)
While sr.Peek <> -1
TextBox1.AppendText(sr.ReadLine() & vbCrLf)
End While
sr.Close()
Code was tested against this file:
http://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt[
^]