I cannot convert some books from Simplified Chinese to Traditional Chinese. I find that the text files inside epub are encoded in UTF8. Do you come across that? Here is part of a text file:
<?xml version="1.0" encoding="UTF-8"?>
<html xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ibooks="http://www.apple.com/2011/iBooks" xmlns:m="http://www.w3.org/1998/Math/MathML" xmlns:epub="http://www.idpf.org/2007/ops" xml:lang="zh" xmlns="http://www.w3.org/1999/xhtml"><head><meta charset="utf-8"/><title>未命名</title><link rel="stylesheet" type="text/css" href="assets/css/content1.css"/></head><body><p id="p0" class="s1 s2">银币故事</p><p id="p1" class="s3 s4"><img class="s5" width="200" height="180" src="assets/images/730689864.jpg" id="image-31" alt=""/></p><p id="p2" class="s3 s4"><img class="s5" width="200" height="182" src="assets/images/809711190.jpg" id="image-32" alt=""/></p><p id="p3" class="s6 s7">*</p><p id="p4" class="s6 s7">公元前527年至&#x 524D;430年，古代希&# x814A;城邦国家雅 178;铸造的货币Ծ B;四德拉克马银 币。银币正面&# x662F;头戴皮盔的 973;神雅典娜头Ԍ F;，背面是雅典 娜女神的守护&# x8005;猫头鹰。</p><p id="p5" class="s6</p></body></html>