Django : translation not found only during tests

Question

I'm doing functional tests (Selenium) on my django app, and I want to include some fixtures. So first, I tried to load fixtures using manage.py:

./manage.py dumpdata > db.json
./manage.py loaddata db.json

No errors, I decided to use this data for my tests:

class FrontTest(LiveServerTestCase):

    fixtures = ['db.json']

But when I ran my test:

django.core.serializers.base.DeserializationError: Problem installing fixture '/srv/app/db.json': EventBlock has no field named 'content_fr'

Have you ever get this error ?

Thank you in advance.