When upgrading from 2.5.8 to 2.6.1 the Translator component does not seem to be compatible with the "sticky locale" from the cookbook article.

The difference with my implementation is that I use services.yml in order to make the call, instead of implementing the EventSubscriberInterface.

services:
    acme.locale_listener:
        class: Acme\DemoBundle\EventListener\LocaleListener
        tags:
            - { name: kernel.event_listener, event: kernel.request, method: setLocaleForUnauthenticatedUser }

Injecting the Translator into the Listener and setting the locale manually does solve the problem. Re-adding the code that is removed by this commit of Sept 26 also does result in the expected behaviour again.

Has the behaviour changed, or is this behaviour wanted?