To override the default list of 600+ languages add a configuration entry to your settings/local.py like so:
DOCUMENTS_LANGUAGE_CHOICES = [('eng', 'English'), ('deu', 'German')]
to make the list translatable import ugettext_lazy and enclose the language name with _():
from django.utils.translation import ugettext_lazy as _
DOCUMENTS_LANGUAGE_CHOICES = [('eng', _('English')), ('deu', _('German'))]