Change record status: 
Project: 
Introduced in branch: 
8.0.x
Introduced in version: 
8.0.0-beta13
Description: 

All three menu links classes supported a title_arguments key earlier which allowed providing a list of translation arguments (eg. @count) as part of the plugin definition. That raised caching concerns because it would of course depend on dynamic data (and possibly even an external object or more external objects) and was therefore removed.

If you need a title for any LocalActionDefault, LocalTaskDefault and ContextualLinkDefault derivatives, use StringTranslationTrait and pass in dynamic arguments appropriately, see https://www.drupal.org/node/2540342

Impacts: 
Module developers