Hello @visiblezinnia
Chinese is not included in the character set of the font that is used for the Simple template (Open Sans). This will require the use of another font. You can set up a custom font yourself, using the instructions from the documentation: Using custom fonts.
If you have a paid license of one of the PDF invoice extensions, we have a Chinese language pack that will use a Chinese font automatically so that you don’t need to make any customizations yourself – send us an email at [email protected] if you do!
Hope that helps!