In this iteration, we’ve modified the routes, adding a constraint via: :all(I guess the default is via: :get) to the root declarations. I didn’t notice that, simple moving the root declarations into a :locale scope at first. It works until iteration J4: add a Locale Switcher. I encounter a No route matches [POST] “/en” error when changing locale without that modification. I think it would be more straightforward to move that modification to iteration J4 and give some explanation.