Where to put response messages in laravel api?

In my laravel 5.5 api I have a lot of response message like "You successfully completed some action..".

At the moment I have stored them as constants in the controller they are used. I want to move all of them to a single location, so if I need to change them later I don't have to hunt for them in each controller.

What is the best approach for this usecase?

via Chebli Mohamed