Your readers like your article, and you also like to hear what they think of. But in most cases what you want is a descriptive and detailed content in the discussion instead of “Thank you”, “Great article”, etc.

So you probably want to limit the minimal comment length in your wordpress blog. This is what we are going to talk about.

The solution is pretty simple, just put following codes to your functions.php and you’re done.

/** 
 * Limit minimul length of comment content in wordpress
 * http://clonetemplates.com/?p=530
 */ 
add_action( 'preprocess_comment', 'ct_minimul_comment_length', 8 );

function ct_minimul_comment_length( $commentdata ){
	$minlength = 20;//minimal length you want to limit the comment content
	preg_match_all( '/./u', trim( $commentdata['comment_content'] ), $maxlength );
	$maxlength = count( $maxlength[0] );
	if( $maxlength < $minlength ) {
		wp_die( sprintf(_('Come on buddy, say at least %s characters', 'ct'), $minlength ));
	}
	return $commentdata;
}

Limit minimal length of comment content in wordpress

Reference: preprocess_comment