If a text or html file is uploaded which contains Unicode characters, but not UTF-8 encoding, it will not be displayed correctly if the user attempts to "Edit Content" in resources. Only UTF-8 encoding is typically supported in web applications.
There isn't an easy solution (that I can think of). Some possibiities:
1) Test for correct encoding on files when uploaded or edited – but this would likely be unacceptably slow.
2) Always display a warning in the edit window that non-UTF-8 content will not be displayed correctly.
One way to reproduce this problem is to create a MS Word document with non-Latin characters, and save as Unicode Text UTF-16).