...
Edit /etc/apache2/conf-available/04omk-proxy.conf
and add the following lines
<Location "/zh">
ProxyPass http://localhost:8042/zh retry=5
ProxyPassReverse http://localhost:8042/zh
ErrorDocument 503 '<html><head><meta http-equiv="refresh" content="60"></head><body><h1>Temporary Service Interruption</h1>The requested OMK page should be back soon. This page will automatically reload in 60 seconds.</body></html>'
</Location>
...
sudo systemctl restart omkd
Reference
The Language module for simplified chinese - zh.pm:
This gets placed in two places by the installer:
/usr/local/omk/lib/Opmantek/I18N/zh.pm
/usr/local/omk/lib/.tmp/PAR/VendorLibs.pm.exe/lib/DateTime/Locale/zh.pm