I think the problem is that utf-8 encoded content is expected. The relavent code is this:
StreamReader sr = file.OpenText();
this.lblInclude.Text = sr.ReadToEnd();
file.OpenText() opens a StreamReader with utf-8 encoding to read the contents of the text file.
I'm not sure if there is a solution other than to encode your content as utf-8. I'm really no expert on character sets and encoding, but my understanding is that utf-8 supports many languages, but I think yor content files are not in utf-8 and would need to be converted to utf-8 to work with the existing code.
Hope it helps.
If you find a solution, please let me know.