WooCommerce - Change order button text strings

functions.php

<?php // Do not include this if already open!

/**
 * Code goes in theme functions.php.
 */
add_filter( 'gettext', 'custom_order_button_strings', 20 );

/**
 * Change order button text strings.
 *
 * @link http://codex.wordpress.org/Plugin_API/Filter_Reference/gettext
 */
function custom_order_button_strings( $translated_text ) {
	switch ( $translated_text ) {
		case 'Proceed to HBL' :
			$translated_text = __( 'Pay via HBL', 'woocommerce-hbl' );
			break;
	}
	return $translated_text;
}