Multibyte characters don't get rendered when conversion sandbox enabled

Issue Summary

Multibyte characters don't get rendered when conversion sandbox enabled even when appropriate font is installed with the following steps.
https://confluence.atlassian.com/confkb/non-ascii-characters-display-as-square-characters-in-confluence-317948797.html

Environment

• Confluence Data Center
• document.conversion.sandbox.disable=false (same as default)
• Multibyte font installed on the server
  • "4 fonts package" of Japanese IPA fonts (https://ipafont.ipa.go.jp/old/ipafont/download.html#en) installed in
    • /usr/share/fonts
    • /opt/atlassian/confluence/jre/lib/fonts/fallback
  • Following JVM argument is specified in setenv.sh

    CATALINA_OPTS="-Dconfluence.document.conversion.fontpath=/usr/share/fonts/ -Dconfluence.document.conversion.slides.defaultfontname.regular=IPAGothic -Dconfluence.document.conversion.slides.defaultfontname.asian=IPAGothic -Dconfluence.document.conversion.slides.defaultfontname.symbol=IPAGothic ${CATALINA_OPTS}"
    CATALINA_OPTS="-Dconfluence.document.conversion.words.defaultfontname=IPAGothic ${CATALINA_OPTS}"
    

Steps to Reproduce

1. Install Japanese fonts on the hosting server as described in above.
2. Start a Confluence Data Center instance
3. Attach テスト.pptx in an editor

Expected Results

"テストプレゼンテーション" is shown in thumbnail and preview.

Actual Results

Square characters are shown for thumbnail and preview.

• Thumbnail
  

• Preview
  

Notes

Characters are rendered correctly for some file type.
As far as I confirmed in 6.12.2,

file type	thumbnail	preview
pptx
docx
xlsx
txt

Workaround

Disable the conversion sandbox adding following option in setenv.sh. This is not recommended as it will affect the stability of the instance.

CATALINA_OPTS="-Ddocument.conversion.sandbox.disable=true ${CATALINA_OPTS}"

Solution

Add the following to setenv.sh so that system settings are correctly propagated to the sandbox:

CATALINA_OPTS="-Dconversion.sandbox.java.options=-Dconfluence.document.conversion.slides.defaultfontname.regular=IPAGothic,-Dconfluence.document.conversion.slides.defaultfontname.asian=IPAGothic,-Dconfluence.document.conversion.slides.defaultfontname.symbol=IPAGothic,-Dconfluence.document.conversion.words.defaultfontname=IPAGothic  ${CATALINA_OPTS}"