Django "settings.DATABASES is improperly configured" and "ImproperlyConfigured at /i18n/setlang/"

Question

I wrote a django web application and now I need to translate it to english. I followed the documentation but I keep getting this strange error:

ImproperlyConfigured at /i18n/setlang/ settings.DATABASES is improperly configured. Please supply the ENGINE value. Check settings documentation for more details. Request Method: POST Request URL: http://192.92.149.139:8000/i18n/setlang/ Django Version: 2.0.3 Exception Type: ImproperlyConfigured Exception Value:
settings.DATABASES is improperly configured. Please supply the ENGINE value. Check settings documentation for more details. Exception Location: /home/mwon/venvs/arquivo/lib/python3.6/site-packages/django/db/backends/dummy/base.py in complain, line 20 Python Executable: /home/mwon/venvs/arquivo/bin/python3.6 Python Version: 3.6.4 Python Path: ['/home/mwon/digitalocean/website_dev', '/home/mwon/venvs/arquivo/lib/python36.zip', '/home/mwon/venvs/arquivo/lib/python3.6', '/home/mwon/venvs/arquivo/lib/python3.6/lib-dynload', '/usr/lib/python3.6', '/home/mwon/venvs/arquivo/lib/python3.6/site-packages', '/home/mwon/venvs/arquivo/lib/python3.6/site-packages/django_styleguide-1.2.5-py3.6.egg', '/home/mwon/venvs/arquivo/lib/python3.6/site-packages/Markdown-2.6.11-py3.6.egg', '/home/mwon/venvs/arquivo/lib/python3.6/site-packages/bs4-0.0.1-py3.6.egg', '/home/mwon/venvs/arquivo/lib/python3.6/site-packages/beautifulsoup4-4.6.0-py3.6.egg', '/home/mwon/venvs/arquivo/lib/python3.6/site-packages/duc_preprocess-1.0-py3.6.egg', '/home/mwon/venvs/arquivo/lib/python3.6/site-packages/simple_cnlp-1.0-py3.6.egg', '/home/mwon/venvs/arquivo/lib/python3.6/site-packages/django_mongoengine-0.3-py3.6.egg'] Server time: Qua, 5 Set 2018 11:21:17 +0000

EDIT: and the settings.DATABASES:

{
    'default': {
        'ENGINE': 'django.db.backends.dummy',
        'ATOMIC_REQUESTS': False,
        'AUTOCOMMIT': True,
        'CONN_MAX_AGE': 0,
        'OPTIONS': {},
        'TIME_ZONE': None,
        'NAME': '',
        'USER': '',
        'PASSWORD': '',
        'HOST': '',
        'PORT': '',
        'TEST': {
            'CHARSET': None, 'COLLATION': None, 'NAME': None, 'MIRROR': None
        }
    }
}

This is my urls.py:

urlpatterns = [
    path('i18n/',include('django.conf.urls.i18n')),
]

urlpatterns += i18n_patterns(
    path('admin/',admin.site.urls),
    path('',include('arquivo.urls')),
    prefix_default_language = True
)

and settings.py:

LANGUAGE_CODE = 'pt'    
LANGUAGES = (
    ('en', 'English'),
    ('pt', 'Portuguese'),
)
USE_I18N = True
LOCALE_PATHS = [
    os.path.join(BASE_DIR,'locale')
]

The translation seems to be working fine. The problem was when I included a form to select the language. I used the example code from documentation:

{% load i18n %}

<form action="{% url 'set_language' %}" method="post">{% csrf_token %}
    <input name="next" type="hidden" value="{{ redirect_to }}">
    <select name="language">
        {% get_current_language as LANGUAGE_CODE %}
        {% get_available_languages as LANGUAGES %}
        {% get_language_info_list for LANGUAGES as languages %}
        {% for language in languages %}
            <option value="{{ language.code }}"{% if language.code == LANGUAGE_CODE %} selected{% endif %}>
                {{ language.name_local }} ({{ language.code }})
            </option>
        {% endfor %}
    </select>
    <input type="submit" value="Go">
</form>

Answer 1

Ok, so the problem was related with sessions. I'm using a MongoDB database with Django-MongoEngine and didn't turn on sessions support. So just added these two lines of code

SESSION_ENGINE = 'django_mongoengine.sessions'
SESSION_SERIALIZER = 'django_mongoengine.sessions.BSONSerializer'

to settings.py and everything started to work fine.