Debezium prescribe using of UTF-8 for database.
When a string arrives it is decoded by pgoutput decoder in
io.debezium.connector.postgresql.connection.pgoutput.PgOutputMessageDecoder.readColumnValueAsString(ByteBuffer)
Unfortunately the coming valus is UTF-* but the conversion is platform specific so if the system is not using UTF-8 as the default one then the string is garbled.

Workaround - when Kafka Connect is started, set env variable KAFKA_OPTS=-Dfile.encoding=UTF-8 which switches default JVM encoding.