Steps to replicate the issue :

• Export a document in any format, say PDF or EPUB.
• The exported file failed to display characters inside LanguageConverter markups (-{}-).

Introduction of LanguageConverter markups in MediaWiki:
https://www.mediawiki.org/wiki/Writing_systems/Syntax

Example: https://zh.wikisource.org/wiki/%E9%98%BF%E6%88%BF%E5%AE%AE%E8%B3%A6?uselang=en

The exported file omits characters in -{}-.
Web: 六王畢，四海一。蜀山兀，阿房出。覆壓三百餘里，隔離天日。驪山北構而西折，直走咸陽。
Exported file: 六王畢，四海一。蜀山兀，阿房出。覆壓三百餘里，隔離天日。驪山北構而西折，直走陽。
("咸" is omitted as it is in the markup -{}-)