When you write the message file, start it with the statements:
$quote x $set 1
where x is the character you wish to use as a quote character.
Then, write each message in the format:
$ nnnnn "your message here"
where the double-quote character (") is assumed to be the quote character set in the $quote statement above. You can change quote statements at any point in the message file; each change applies to all the messages which follow it up until the next $quote statement.