Hello,
These two are separate from the translation file problem.
For the sale method: on the page you linked, the price ends with
<span class="hikashop_product_price_per_unit"> l'unité</span>
and that is exactly what HikaShop's own listing_price.php outputs, we compared it with a clean 6.5.2. The modification from our FAQ replaces that whole span, so the file being used on your website does not carry the modification anymore. Please check it via the menu Display > Views: select the template of your website at the top of the page, then open the file product / listing_price.php. If the modification is gone from it, putting it back should bring your sale methods back.
Note that the next version adds a "Price unit label" setting directly on the product edit page. It replaces the " each" text for that product without touching any file, and you can enter the name of a translation there so that the label follows the language of the visitor. So you will be able to drop the custom field and the view modification entirely.
For the amount: we set up an item custom field with the column name "amount" on a clean HikaShop 6.5.2 and the amount entered is indeed the price used in the cart, so the mechanism still works in your version. Two things to check on your side:
- the plugin "System - Custom price" is enabled in the Joomla plugins manager
- its "Column name of the field" option still says amount