Implement multilanguage

This completes the multilanguage support

For this a new setting in the config got added "defaultLanguage"

config.sample.php

@@ -1,18 +1,25 @@
 <?php
-
 $config = [
     "homeserver" => "example.com",
     "access_token" => "To be used for sending the registration notification",
+
     // Which e-mail-adresse shall the bot use to send e-mails?
     "register_email" => 'register_bot@example.com',
     // Where should the bot post registration requests to?
     "register_room" => '$registerRoomID:example.com',
+
     // Where is the public part of the bot located? make sure you have a / at the end
     "webroot" => "https://myregisterdomain.net/",
+
     // optional: Do you have a place where howTo's are located? If not leave this value out
     "howToURL" => "https://my-url-for-storing-howTos.net",
+
     // When you want to collect the password on registration set this to true
     "getPasswordOnRegistration" => false,
+
+    // default language: one of [ en-gb | de-de ]
+    "defaultLanguage" => "en-gb",
+
     // to define where the data should be stored:
     "databaseURI" => "sqlite:" . dirname(__FILE__) . "/db_file.sqlite",
     // credentials for sqlite not used