Overriden Language define not working...

Hei.. Question..

I'm trying to install a mod <Order Steps Edition 2 v1.3x>.

It's working now.. but I am curious about why the overriden language
define that I've written is not working.

The installation instruction says that I have to add these code to

/includes/languages/english.php

// Order Steps Edition 2
define('TEXT_ORDER_STEPS_1', 'Shipping Method');
define('TEXT_ORDER_STEPS_2', 'Payment Method');
define('TEXT_ORDER_STEPS_3', 'Review Order');
define('TEXT_ORDER_STEPS_4', 'Order Complete');

Because I am trying to adhere to the overriding rule to make
upgrade easier for later I put these codes to my custom template
language directory which is :

includes\languages\simple_zen\english.php

Strangely it does not work... I've written the define code into

/includes/languages/english.php

and this works..

Other language changes I've done in

includes\languages\simple_zen\english.php

works..

Strange...

Thanks,
Deddy