As written, your initdb command sets the default encoding to SQL-ANSI. To set the default as UTF8, you need to do this, instead:
sudo su postgres -c '/opt/local/lib/postgresql92/bin/initdb -E UTF8 -D /opt/local/var/db/postgresql92/defaultdb'
Note: The above command is supposed to be on one line. Also, the order of the parameters is important. The encoding must come before the location of the database files. This is also true for postgreSQL93, which is what I actually installed.