Added cookbook recipe for lang setting without additional route param

doc/book/cookbook/bookdown.json

@@ -7,6 +7,7 @@
         {"Registering custom view helpers when using zend-view": "using-custom-view-helpers.md"},
         {"Using zend-form view helpers": "using-zend-form-view-helpers.md"},
         {"Using Expressive from a subdirectory": "using-a-base-path.md"},
-        {"Building modular applications": "modular-layout.md"}
+        {"Building modular applications": "modular-layout.md"},
+        {"Setting up locale without additional routing parameter": "setting-locale-without-routing-parameter.md"}
     ]
 }

doc/book/cookbook/setting-locale-without-routing-parameter.md

@@ -0,0 +1,182 @@
+# How can I setup the locale without an additional parameter?
+
+It is a common task to have a localized web application where the setting of
+the locale (and therefore the language) depends on the routing. In this recipe 
+we will automatically add the language to the route without changing all of 
+the existing routes.
+
+## Setup a middleware to extract the language from the URI ##
+
+First, we need to setup a middleware that extracts the language param directly
+from the request URI. If if doesn't find any it sets a default. If it does
+it uses the language to setup the locale. It also amends the request to add
+the language as an attribute. 
+
+```php
+namespace Application\I18n;
+
+use Locale;
+use Zend\Expressive\Helper\UrlHelper;
+
+class SetLanguageMiddleware
+{
+    private $helper;
+
+    public function __construct(UrlHelper $helper)
+    {
+        $this->helper = $helper;
+    }
+
+    public function __invoke($request, $response, callable $next)
+    {
+
+        $uri = $request->getUri();
+
+        $path = $uri->getPath();
+
+        if (! preg_match('#^/(?P<lang>[a-z]{2})/#', $path, $matches) {
+            Locale::setDefault('de_DE');
+            return $next($request, $response);
+        }
+
+        $lang = $matches['lang'];
+        Locale::setDefault($lang);
+        $this->helper->setBasePath($lang);
+
+        return $next(
+            $request->withUri(
+                $uri->withPath(substr($path, 3))
+            ),
+            $response
+        );
+    }
+}
+```
+
+Then you will need a factory for the `SetLanguageMiddleware` to inject the
+`UrlHelper` instance.
+
+```php
+namespace Application\I18n;
+
+use Interop\Container\ContainerInterface;
+use Zend\Expressive\Helper\UrlHelper;
+
+class SetLanguageMiddlewareFactory
+{
+    public function __invoke(ContainerInterface $container)
+    {
+        $urlHelper = $container->get(UrlHelper::class);
+
+        return new SetLanguageMiddleware($urlHelper);
+    }
+}
+```
+
+
+Afterwards you need to configure the `SetLanguageMiddleware` in your 
+`/config/autoload/middleware-pipeline.global.php` file so that it is executed 
+on every request.
+
+```php
+return [
+    'dependencies' => [
+        'factories' => [
+            Application\I18n\SetLanguageMiddleware::class =>
+                Application\I18n\SetLanguageMiddlewareFactory::class,
+        ],
+    ]
+
+    'middleware_pipeline' => [
+        'pre_routing' => [
+            [
+                'middleware' => [
+                    Application\I18n\SetLanguageMiddleware::class,
+
+                    /* ... */
+                ],
+            ],
+        ],
+
+        'post_routing' => [
+        ],
+    ],
+];
+```
+
+## Url generation in the view ##
+
+Since the `UrlHelper` has the language set as a base path you don't need 
+to worry about generating URLs within your view. Just use the helper to 
+generate an URL and it will do the rest.
+
+```php
+<?php echo $this->url('your-route') ?>
+```
+
+## Redirecting within your middleware ##
+
+If you want to add the language parameter when creating URIs within your 
+action middleware you just need to inject the `UrlHelper` into your 
+middleware and use it for URL generation:
+
+```php
+namespace Application\Action;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Zend\Diactoros\Response\RedirectResponse;
+use Zend\Expressive\Helper\UrlHelper;
+
+class RedirectAction
+{
+    private $helper;
+
+    public function __construct(UrlHelper $helper)
+    {
+        $this->helper = $helper;
+    }
+
+    /**
+     * @param ServerRequestInterface $request
+     * @param ResponseInterface      $response
+     * @param callable|null          $next
+     *
+     * @return RedirectResponse
+     */
+    public function __invoke(
+        ServerRequestInterface $request,
+        ResponseInterface $response,
+        callable $next = null
+    ) {
+        $routeParams = [ /* ... */ ];
+
+        return new RedirectResponse(
+            $this->helper->generate('your-route', $routeParams)
+        );
+    }
+}
+```
+
+Of course you will need a factory as well to inject the `UrlHelper` into
+the `RedirectAction` middleware:
+
+Then you will need a factory for the `SetLanguageMiddleware` to inject the
+`UrlHelper` instance.
+
+```php
+namespace Application\Action;
+
+use Interop\Container\ContainerInterface;
+use Zend\Expressive\Helper\UrlHelper;
+
+class SetLanguageMiddlewareFactory
+{
+    public function __invoke(ContainerInterface $container)
+    {
+        $urlHelper = $container->get(UrlHelper::class);
+
+        return new RedirectAction($urlHelper);
+    }
+}
+```