Hi,
First, you need to add that content element file in joomfish (you have an installer in joomfish for these files).
Then, for each product, you can add the main language image/file in the edition screen of the product.
Then, you can upload the corresponding image/file of other languages in the upload folder (for images it's media/com_hikashop/upload by default and for files it's media/com_hikashop/upload/safe by default ).
Finally, in joomfish, you can edit the image/file entries and change the file path accordingly to the language.
And voilà, on the front end, the image will be different based on the language.