In your wp-config.php set the encoding constants correctly:
define( 'DB_CHARSET', 'utf8' );
define( 'DB_COLLATE', 'utf8_general_ci' );
And add an accept-charset attribute to your form:
<form
name="frm"
method="post"
action="<?php bloginfo('url'); ?>/message/"
accept-charset="utf8"
>