Moodle Language synchronisation

Hi I recently got used to moodle http://moodle.org. I want to use the official Moodle App for IOs/Android. However I want the language to be german when using the app. Here is an example screenshot:  The docs say that I have to upload a mobile.php to my lang/en folder in order to customize the language of the app. See http://docs.moodle.org/24/en/Mobile_app#Translation (applies for newer versions as well). The file is structured like this <?php $string['about'] = 'About'; full file can be viewed under: http://pastebin.com/5TJWZ4ue However if I upload this file to my server, the app does not change it's language. It is still english. I hope that someone with more insight to moodle can help me.