Steps to reproduce the issue

In the back end

• Edit a Menu item, with or without a previous language association
• Use the Association button just beside the Close one
  

Expected result

It is expected to go to the view Multilingual Associations: Edit Associations (Menus > Menu items)

Actual result

The Edit view closes with the green message Menu item saved..

System information (as much as possible)

Joomla 3.9.16 (official release and RC)
Works as expected on 3.9.15, 3.9.14, 3.9.4.

Additional comments

• Related to
  #27941
  as without this patch, it works as expected.
• the Associations tab (second last before Module Assignment) is working as expected.