feat: register a global form theme and switch the locale to German

config/packages/translation.yaml

@@ -1,5 +1,5 @@
 framework:
-    default_locale: en
+    default_locale: de
     translator:
         default_path: '%kernel.project_dir%/translations'
         providers:

config/packages/twig.yaml

@@ -1,5 +1,7 @@
 twig:
     file_name_pattern: '*.twig'
+    # One theme for the whole app, so it is registered globally rather than per-template.
+    form_themes: ['forms.html.twig']
 
 when@test:
     twig: