So I’ve found absolutely nothing about this subject online.

What I’ve done: I successfully programmed a custom admin menu in english for my wordpress backend, according to https://webkul.com/blog/how-to-add-menu-in-wordpress-admin-panel/, so that’s all good.

What I need: If I change the language of the backend (via the user settings in the wordpress backend), every admin menu gets translated to the new (selected) language, except from my custom admin menu, which of course still appears in English. My question is: How / Where do I need to store custom admin menus in other languages, such that they also get their language changed according to the language selected for the backend ??