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How to translate the administration menus?
While you can change the translation for all the strings within the PrestaShop administration, you cannot edit the names of the administration menus (Catalog, Orders, Customers, etc.) and their submenus (Products, Categories, Monitoring, etc.).
This is because these strings are not part of the translation files, but are stored directly within the database. In order to change it, you must go to the "Menus" page of the "Administration" menu.
This page displays a list of all the top-level menus in your administration, and you can also display their submenus by clicking on the "+" icon in the "Action" column.
From there, you can click on the "edit" icon for the menu or submenu you wish the change the name of. In the page that displays, click the flag next to the "Name" field in order to choose the languages for wish you want to translate the menu (you must have the target language already installed!), or directly change the name in the current language.
Save your changes: the administration is immediately updated with your new translation.
Note that this means you cannot send your menu translation to another shop. The manager of that other shop must perform these steps himself.