Covered by unit tests.   Setup: Create a course with a student and a teacher. As the teacher create an assignment that allows "Online text" submissions and "Annotate PDF" as a feedback type. As a student submit some text. Grade the student and add a "feedback comment" to the submitted file of "Testing example: בקלות ואמנות" and draw a picture. Save the changes. Test: Verify as a student that when you access the assignment download the feedback PDF file, the hebrew characters appear in the pdf file and not not replaced with square symbols. Also verify that the online version does the same thing (the "View annotated PDF" link).