Using Document Generator, Japanese fonts are not supported when exporting in PDF

Description
When exporting templates that contain characters in japanese fonts, the generated PDF document is generated with rectangles instead of said characters.

How to reproduce

1. Add japanese characters to, for instance, the issue description or summary.
2. Export using a template that contains the description or summary

Actual result/Attachments
Some characters appear as squares.

Expected result
Characters should appear correctly, like in the example below.