How to modify WooCommerce button text in default and additional languages

You could use their filter to do this:

/* Add to the functions.php file of your theme */

add_filter( 'woocommerce_order_button_text', 'woo_custom_order_button_text' ); 

function woo_custom_order_button_text() {
    return __( 'Your new button text here', 'woocommerce' ); 
}