Multilingual content: Menu link is not correctly stored on translation.

Problem/Motivation

When I translate node, the translated menu link item overwrites the original menu item link.

This issue was supposedly fixed here: https://www.drupal.org/project/drupal/issues/2599594, but I am still seeing it in 8.9.13

Steps to reproduce :

1. Enable the translation for a content type
2. Enable translation for menu links for that content type
3. Create a node in the default language and on the node creation form, click "Provide a menu link" and add a menu link
4. Translate this node to French and translate the menu link
5. BOTH translations (the default and the French translation) now have the French translation's menu link.

The only way to have a translated menu link is to create it directly from the menu configuration.

Setting priority as major due to lost user input from this bug.