<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>

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',
];

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

     session(['my_locale' => Request::Input('locale')]);

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

<?php namespace AppHttpMiddleware;

use Closure;
use IlluminateHttpRequest;
use IlluminateFoundationApplication;

class Language {

    public function __construct(Application $app, Request $request) {
        $this->app = $app;
        $this->request = $request;
    }

    /**
     * Handle an incoming request.
     *
     * @param  IlluminateHttpRequest  $request
     * @param  Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        $this->app->setLocale(session('my_locale', config('app.locale')));

        return $next($request);
    }

}

protected $middleware = [
   AppHttpMiddlewareLanguage::class,
];

'available_locale' => ['fr', 'gr', 'ja'],

public function handle($request, Closure $next)
{
      if(in_array($request->segment(1), config('app.available_locale'))){
            $this->app->setLocale($request->segment(1));
      }else{
            $this->app->setLocale(config('app.locale'));
      }

      return $next($request);
}

if(in_array($request->segment(1), config('app.available_locale'))){
  $locale = $request->segment(1);
}else{
  $locale = null;
}
Route::group([
   'middleware' => 'web',
   'namespace' => $this->namespace,
   'prefix' => $locale
], function ($router) {
     require base_path('routes/web.php');
});

<?php

namespace AppHttpMiddleware;

use Closure;

class SetLocale
{
     /**
      * Handle an incoming request.
      *
      * @param  IlluminateHttpRequest  $request
      * @param  Closure  $next
      * @return mixed
      */
    public function handle($request, Closure $next)
    {
        if (strpos($request->getHttpHost(), 'fr.') === 0) {
            App::setLocale('fr');
        } else {
            App::setLocale('en');
        }
        return $next($request);
    }
}

protected $middlewareGroups = [
    'web' => [
        // ...
        AppHttpMiddlewareSetLocale::class,
        // ...
    ]
];

Route::group(['domain' => 'fr.' . config('app.root-domain')], function () {
    Route::get('a-propos', 'HomeController@about');
    // ...
}
Route::group(['domain' => config('app.root-domain')], function () {
    Route::get('about', 'HomeController@about');
    // ...
}