add german informal language

resources/lang/de_informal/activities.php

@@ -0,0 +1,23 @@
+<?php
+$de_formal = (include resource_path() . '/lang/de/' . basename(__FILE__));
+
+$de_informal = [
+
+    /**
+     * Activity text strings.
+     * Is used for all the text within activity logs & notifications.
+     */
+
+    // Pages
+ 
+    // Chapters
+   
+    // Books
+    
+    // Bookshelves
+    
+    // Other
+    
+];
+
+return array_replace($de_formal, $de_informal);