Unknown language code am

When adding the app Orfox from the GuardianProject to a repo, I get the following error message (am stands for Amharic):

File "/home/nico/.local/lib/python3.4/site-packages/django/utils/translation/__init__.py" in get_language_info
  245.         lang_info = LANG_INFO[lang_code]

During handling of the above exception ('am'), another exception occurred:

File "/home/nico/.local/lib/python3.4/site-packages/django/core/handlers/exception.py" in inner
  41.             response = get_response(request)

File "/home/nico/.local/lib/python3.4/site-packages/django/core/handlers/base.py" in _get_response
  217.                 response = self.process_exception_by_middleware(e, request)

File "/home/nico/.local/lib/python3.4/site-packages/django/core/handlers/base.py" in _get_response
  215.                 response = response.render()

File "/home/nico/.local/lib/python3.4/site-packages/django/template/response.py" in render
  107.             self.content = self.rendered_content

File "/home/nico/.local/lib/python3.4/site-packages/django/template/response.py" in rendered_content
  84.         content = template.render(context, self._request)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/backends/django.py" in render
  66.             return self.template.render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in render
  207.                     return self._render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in _render
  199.         return self.nodelist.render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/loader_tags.py" in render
  177.             return compiled_parent._render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in _render
  199.         return self.nodelist.render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/loader_tags.py" in render
  72.                 result = block.nodelist.render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/defaulttags.py" in render
  216.                     nodelist.append(node.render_annotated(context))

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in render
  1040.             output = self.filter_expression.resolve(context)

File "/home/nico/.local/lib/python3.4/site-packages/django/template/base.py" in resolve
  736.                 new_obj = func(obj, *arg_vals)

File "/home/nico/.local/lib/python3.4/site-packages/django/templatetags/i18n.py" in language_name
  268.     return translation.get_language_info(lang_code)['name']

File "/home/nico/.local/lib/python3.4/site-packages/django/utils/translation/__init__.py" in get_language_info
  252.             raise KeyError("Unknown language code %s." % lang_code)

Exception Type: KeyError at /repo/1/app/2/
Exception Value: 'Unknown language code am.'