Problem:

You have an EPUB file encoded with a wrong language tag.
Therefore when you use the Read aloud feature of the Google Play Books application the book is read aloud in a wrong language.

Solution:

1. Download the EPUB file to a PC.
2. Change the extension from EPUB to ZIP.
3. Open the .ZIP file.
4. Open the content.opf file using the Notepad app.
5. If you cannot file this content.opf file then please navigate to the OEBPS folder.
6. Find the tag <dc:language> and change its value (e.g. from <dc:language>en</dc:language>to <dc:language>vi</dc:language>).
7. If you cannot find the tag <dc:language> then just add a new tag right above the </metadata> tag (e.g.
   <dc:language>vi</dc:language>
</metadata>
8. Save the content.opf file and rezip the EPUB file.
9. Change the file extension from ZIP to EPUB.