EPUB supports UTF-8 and UTF-16 file encodings. This is not normally something you will have to deal with, but perodically you may have a need to ensure that your files are encoded correctly.
Most files in your EPUB package will be encoded in UTF-8. This is a very common encoding that is not hard to apply to the file in question. Here is what you need to do:
1. Unzip your EPUB. For more information, please see the Zipping an EPUB page.
2. Open the file. You can use just about any text or code editor for this. We like Sublime Text, but you can also use Notepad, TextWrangler, BBEdit, and other text editors. Do not use Microsoft Word, Apple Pages, or any other document editing program.
3. Save As UTF-8 without the BOM. Most editors will have a Save As feature that allows you to change the encoding. Just keep the file name the same, and choose UTF-8 from the list. If it has an option for the Byte Order Marker (BOM), save the file without that.
4. Re-zip your EPUB. Once you have saved the file with the correct encoding, you can re-zip your EPUB file. For more information, please see the Zipping an EPUB page.
Note that encoding errors sometimes occur when you have Unicode characters in your HTML files (like Ā). In some cases, it may be useful to replace those bare Unicode characters with entities (like Ā).