Update Language.php

* added locale detection and switch to preferred language.

app/Http/Middleware/Language.php

@@ -3,6 +3,7 @@
 namespace App\Http\Middleware;
 
 use Closure;
+use Illuminate\Contracts\Session\Session;
 
 class Language
 {
@@ -13,12 +14,27 @@ class Language
      * @param  \Closure  $next
      * @return mixed
      */
+    const SESSION_KEY = 'locale';
+    const LOCALES = ['en', 'de','da'];
+
     public function handle($request, Closure $next)
     {
-        if ($request->session()->exists('locale')) {
-            \App::setLocale(\Session::get('locale'));
+        /** @var Session $session */
+        $session = $request->getSession();
+
+        if (!$session->has(self::SESSION_KEY)) {
+            $session->put(self::SESSION_KEY, $request->getPreferredLanguage(self::LOCALES));
         }
 
+        if ($request->has('lang')) {
+            $lang = $request->get('lang');
+            if (in_array($lang, self::LOCALES)) {
+                $session->put(self::SESSION_KEY, $lang);
+            }
+        }
+
+        app()->setLocale($session->get(self::SESSION_KEY));
+
         return $next($request);
     }
 }