Example of Laravel localization provider

Added new cfg to app.php

<?php // after locale

    'additional_locales' => ['de'],

Extended Application.php

<?php

namespace App\Core;

class Application extends \Illuminate\Foundation\Application
{
    public function getLocalePrefix($locale_to = null) {
        if ($locale_to === null) {
            $locale = self::getLocale();
        } else {
            $locale = $locale_to;
        }
        if ($locale === config('app.fallback_locale')) {
            $lang_prefix = '';
        } else {
            $lang_prefix = $locale;
        }
        return $lang_prefix;
    }
}

Extended UrlGenerator.php

<?php

namespace App\Core;

use Illuminate\Support\Facades\App;

class UrlGenerator extends \Illuminate\Routing\UrlGenerator
{
    /**
     * Generate an absolute URL to the given path.
     *
     * @param  string  $path
     * @param  mixed  $extra
     * @param  bool|null  $secure
     * @return string
     */
    public function to($path, $extra = [], $secure = null)
    {
        $path = App::getLocalePrefix() . $path;

        return parent::to($path, $extra, $secure);
    }
}

new file LocaleServiceProvider.php

<?php // new file

namespace App\Providers;

use App\Core\UrlGenerator;
use Illuminate\Support\Facades\App;
use Illuminate\Support\Facades\Auth;
use Illuminate\Support\Facades\Request;
use Illuminate\Support\ServiceProvider;

class LocaleServiceProvider extends ServiceProvider
{
    /**
     * Bootstrap any application services.
     *
     * @return void
     */
    public function boot()
    {
        // detect user language and set app locale
        if (in_array($s1 = Request::segment(1), config('app.additional_locales'))) {
            // 1. set app locale if first URL segment is in additional locales
            App::setLocale($s1);
        } else if (Auth::check()) {
            // 2. user logged in, set language from user profile settings
            // TODO
        } else if (isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
            // 3. detect lang from user agent
            $lang = substr($_SERVER['HTTP_ACCEPT_LANGUAGE'], 0, 2);
            if (in_array($lang, config('app.additional_locales'))) {
                App::setLocale($lang);
            }
        }
        // 4. else Laravel automatically will use fallback_locale
    }

    /**
     * Register any application services.
     *
     * @return void
     */
    public function register()
    {
        $this->app->bind('url', 'App\Core\UrlGenerator');
    }
}

part from RouteServiceProvider.php

<?php // added global prefix
        $router->group(['prefix' => App::getLocalePrefix(), 'namespace' => $this->namespace], function ($router) {
            require app_path('Http/Routes/app_routes.php');
            require app_path('Http/Routes/api_routes.php');
            require app_path('Http/Routes/admin_routes.php');
            require app_path('Http/Routes/dev_routes.php');
        });