Solved it.
on Category.tpl, I had a line with the following parameters:
{include file="./product-list-cat.tpl" products=$subcategory_object->getProducts('1','1','100')}
and replaced it for:
{include file="./product-list-cat.tpl" products=$subcategory_object->getProducts($cart->id_lang,'1','100')}
Just modified: getProducts('1','1','100')
for getProducts($cart->id_lang,'1','100')
, so it makes the product display as multilanguage.