Have you tried declaring the language as 'zh-hant'?
Traditional Chinese ebooks from Kindle Store have language code 'zh-Hant' in KFX format. However you need to use lowercase 'zh-hant' inside 'dc:language' tag in the EPUB's *.opf.
This method doesn't work for most platforms (Eink, Android, iOS), since Amazon deliver KF8 to these devices. Maybe it would work for your Scribe?