You can't just send the char (or UTF8) through the serial port. You have to convert it. First get the length of the char in UTF-8, then get the bytes and send the bytes.
Getting the size of UTF-8: Getting the actual length of a UTF-8 encoded std::string?
Then send it one by one. On the other side you need something to assemble them back.
You could also consider using a better alternative to writing bytes directly to the port, such as http://code.google.com/p/java-simple-serial-connector/