In an effort to streamline the Flarum translations we have changed namespaces one last time and are now under the Flarum official flarum-lang organisation. In that process I have also merged the core translation pack with the third-party translations, so you will only have to enable it once in your admin control panel.
To update, please enter following commands in the root of your Flarum install if you had a previous versions installed (otherwise just follow the instructions in the first post):
composer remove kakifrucht/flarum-de
composer remove kakifrucht/flarum-de-extended
composer require flarum-lang/german
php flarum cache:clear
This update also adds a translation for the user badges extension (thanks @Juba007).