Character Encoding Failure on some Hindi, Nepali and Thai characters from Adobe Illustrator to PDF

[#1]

I have made a poster in Adobe Illustrator. After I have converted it as a PDF, I found that some of my Hindi, Nepali and Thai characters do not pass "Character Encoding" Criteria when doing Accessibility Check. Would there be anyway I should set in the AI file or the PDF file in order to pass "Character Encoding" test? Or would it be an existing bug from Adobe Illustrator?

[#2]

I have made a poster in Adobe Illustrator. After I have converted it as a PDF, I found that some of my Hindi, Nepali and Thai characters do not pass "Character Encoding" Criteria when doing Accessibility Check. Would there be anyway I should set in the AI file or the PDF file in order to pass "Character Encoding" test? Or would it be an existing bug from Adobe Illustrator?

[#3]

Have you tried different font ?

[#4]

Yes, I do try. "Yantramanav" Font set is working for "Character Encoding" problem. However, there's some square bracket in between text when I was making Reading Order. Would there be any font that can work perfectly for both character encoding problem and squares in reading order?