Set minimal character limit before comments being accepted

functions.php

<?php

/*
 *  Set minimal character limit before comments being accepted
 *  @url: http://www.paulund.co.uk/set-minimal-comment-limit-in-wordpress
 * /

add_filter( 'preprocess_comment', 'minimal_comment_length' );
 
function minimal_comment_length( $commentdata ) {
    $minimalCommentLength = 20;
 
  if ( strlen( trim( $commentdata['comment_content'] ) ) < $minimalCommentLength ) 
        {
		wp_die( 'All comments must be at least ' . $minimalCommentLength . ' characters long.' );
        }
	return $commentdata;
}