Laravel 更改语言环境不起作用

I am using a dropdown lists for the languages, consisting of english and dutch.

<form class="" action="{{url('/locale')}}" method="post">
            Locale:
              <select class="" name="locale" onchange="this.form.submit()">

                <option value="en" >English</option>
                <option value="du" >Dutch</option>
              </select>
          </form>

那么这是我的 routes.php，

Route::post('/locale', function(){

     App::setLocale(Request::Input('locale'));

     return redirect()->back();
});

resources/
 /du
   navigation.php
 /en
  /navigation.php

<?php
return [
  "home" => 'Home-test-dutch',  
];

<?php
return [
  "home" => 'Home',  
];