Shopping Cart Designer is purely a design program, so you cannot edit any text in it, period. However, if you have any images, such as buttons, that contain text in another language that you wish to use as page elements, you can import them into your theme in Shopping Cart Designer.
To make changes to your store text, use the options in Shopping Cart Creator. For information about changing the language of your store text in Shopping Cart Creator, read How Do I Add Custom Dictionaries to Shopping Cart Creator?.
