We had recently added better Simplified Chinese support for Treatment Note and Patient History PDFs. However, that's not the only place where we generate PDFs, and not all of those places used the same mechanism behind the scenes. More work remained to be done on that front.
We have just added support for the SimHei Simplified Chinese font in our Letters section. Now, when you export a letter with Simplified Chinese text to the PDF format, that text should show up without issue in the resulting file. We also changed the font providing the Latin character set to match that of the body text in the rest of Cliniko.