You can change your toplinks as from “My cart” to “Shopping cart” from following URL:
See on line number 48 to 52.
and after that overrides the Links.php as follows
<blocks> <checkout> <rewrite> <links>My_Module_Block_Checkout_Links</links> </rewrite> </checkout> </blocks>
and also Change in Links.php
class Mage_Checkout_Block_Links extends Mage_Core_Block_Template to class My_Module_Block_Checkout_Links