Steps to reproduce the issue

In a multilingual site:
Go to Content -> Categories and select a Category to edit that does not have Associations
Note the URL bar:
.../administrator/index.php?option=com_categories&view=category&layout=edit&id=2&extension=com_content
Language is still set to All
Select the Associations button in the Toolbar - there is a warning message and the Versions button disappears
Note the url bar:
.../administrator/index.php?option=com_categories&view=category&layout=edit&id=2com_content
The extension= request key is missing before com_content

Expected result

Normal working toolbar

Actual result

Missing Versions button, Help button produces 404 response, Save seems to work!

System information (as much as possible)

Additional comments

This affects all components with categories with associations.