How can I tell Django to translate (i18n) a file which is not one of the predefined files of a Django app?

I added a python file to the Django app directory. This file is not taken into account when I call manage.py makemessages

my_app
  > migrations
  > templates
  - __init__.py
  - admin.py
  - forms.py
  - models.py
  - my_additional_file.py
  - ...

I use gettext from django.utils.translation like in the all the other python files. Is there an additional configuration where I can include such files? I could not find anything in the documentation.