By the way, I have alter the database character set and national character set to UTF8 before the export form the old database 8.1.7 before the import into the new database 9.2.0. But it still doesn't work and even caused some records to be lost as the columns are too large...
Extracted from my export log:
Export file created by EXPORT:V08.01.07 via conventional path
import done in UTF8 character set and AL16UTF16 NCHAR character set
import server uses AL32UTF8 character set (possible charset conversion)
export server uses UTF8 NCHAR character set (possible ncharset conversion)