If you see question or square marks in the pdf instead of the actual character (most frequently seen in a chinese or arabic character). The problem could be that the font currently used doesn’t support that character.
Why does this happens?
The plugin use a very complete font that covers most of the characters that are used, unfortunately is impossible to have a font that cover all of them so if a character is not covered it is replaced by a question or square mark.
How can this be fixed?
To fix it you can change the font that the plugin uses and pick another that has the characters that you want to use. To do so go to Template Settings/ Appearance and select another default font