Localization for DocumentForm

My `settings.py` has entries for localization:

```
 LANGUAGE_CODE = 'de'
 USE_L10N = True
```

When using `{{ form.as_p }}` in templates for a `DocumentForm` the decimal seperator is not a comma as expected. Forms are created from a `Document` by:

```
class NodeForm(DocumentForm):
    class Meta:
        document = nodeClass
```

How can I enable localization?
