i cannot find where to edit how "Shopping cart" and "0 items" in the header is shown in other languages,
there seems to be just one line in the header.php in template folder for it.

isnt there a line in some file in the includes/languages/"other language" folder?

if it is hard-coded in your header then no, but you can add this text stinge to each language.php file in the includes/languages folder

[php]define("TEXT_SHOPPINGCART","Shopping Cart");[/php]
then add in place of the text
[php]<? echo TEXT_SHOPPINGCART; ?>[/php]
0 products is already there with the define
[php]define('BOX_SHOPPING_CART_EMPTY', '0 products');[/php]
so you can replace the text in your header with an echo of
[php]<? echo BOX_SHOPPING_CART_EMPTY; ?>[/php]