We also tried to do the test on this way:

$this->call('GET', 'http://local.dev');

and

$this->call('GET', 'http://de.local.dev');

But in that case, the ServiceProvider which set the app locale is called before.. (see the next update post)

Our service provider list on config/app/php

    'providers' => [

        /*
         * Laravel Framework Service Providers...
         */
        Illuminate\Foundation\Providers\ArtisanServiceProvider::class,
        Illuminate\Auth\AuthServiceProvider::class,
        Illuminate\Broadcasting\BroadcastServiceProvider::class,
        Illuminate\Bus\BusServiceProvider::class,
        Illuminate\Cache\CacheServiceProvider::class,
        Illuminate\Foundation\Providers\ConsoleSupportServiceProvider::class,
        Illuminate\Routing\ControllerServiceProvider::class,
        Illuminate\Cookie\CookieServiceProvider::class,
        Illuminate\Database\DatabaseServiceProvider::class,
        Illuminate\Encryption\EncryptionServiceProvider::class,
        Illuminate\Filesystem\FilesystemServiceProvider::class,
        Illuminate\Foundation\Providers\FoundationServiceProvider::class,
        Illuminate\Hashing\HashServiceProvider::class,
        Illuminate\Mail\MailServiceProvider::class,
        Illuminate\Pagination\PaginationServiceProvider::class,
        Illuminate\Pipeline\PipelineServiceProvider::class,
        Illuminate\Queue\QueueServiceProvider::class,
        Illuminate\Redis\RedisServiceProvider::class,
        Illuminate\Auth\Passwords\PasswordResetServiceProvider::class,
        Illuminate\Session\SessionServiceProvider::class,
        Illuminate\Translation\TranslationServiceProvider::class,
        Illuminate\Validation\ValidationServiceProvider::class,
        Illuminate\View\ViewServiceProvider::class,



        /*
         * Application Service Providers...
         */
        App\Providers\AppServiceProvider::class,
        App\Providers\EventServiceProvider::class,

        /*
         * Custom from project
         *
         * It should be before the RouteServiceProvider, because
         * the routes definition use the locale configuration
         */
        App\CC\Providers\LocaleServiceProvider::class,

        /*
         * Application Service Providers...
         */
        App\Providers\RouteServiceProvider::class,

        /*
         * Custom from project
         */
        [...]

    ],

And the content of App\CC\Providers\LocaleServiceProvider

    public function boot()
    {
        // Default locale if not one is found
		$locale = Config::get('cc.app.locale.default');

		// we strip the www in mod_rewrite
		$domain = explode('.', $_SERVER['HTTP_HOST'])[0]; // only the first is relevant

		$localeData = $localeConfig->getByDomainOrCode($domain);

		if (!is_null($localeData))
		{
			$locale = $localeData['lang'];
		}

		// set app locale
		$this->app->setLocale($locale);
    }

Any idea? Thanks

UPDATE:

We detected that the HTTP_HOST that the Service Provider receive isn't cc.local.dev or de.cc.local.dev sent by the $this->call(), it is just localhost.. it is executed before the testing call and define the app locale..

Still without ideas of how resolve it