If changing $string = convertEncoding($string, 'latin1', 'UTF-8');
to $string = convertEncoding($string, '', 'UTF-8');
solves the problem then I shall implement that change in my code.
I think that if you are going to use East Asian languages then UTF-8 is the best encoding to use as it appears to cover most combinations. It is already used as the standard encoding for XML files.
I as not aware of the problem with saving files with Windows Notepad, so it may be worth a mention in my article. Do you know if the same problem exists with Wordpad?
As for problems with the mbstring.func_overload option, I have never tried this so I have not encountered any errors. If some problems arise when it is turned on then it would be useful to investigate further to see exactly what is happening. I would be grateful for any information that you could provide.