Why default locale is not fallen back to?

[hopewise]

In my routes, I have:

  Rails.application.routes.draw do
    filter :pagination, :uuid, :locale
  end
 get 'lab' => 'experiments#lab'

however, I got routing error if I tried to visit a route of non-existing locale,
like for example: /ko/lab

any idea?

[exegeteio]

This seems like you may have your get in the wrong location. First, try moving up into the routes:

Rails.application.routes.draw do
  filter :pagination, :uuid, :locale
  get 'lab' => 'experiments#lab'
end

If that does not work, can you post the output of rails routes ?