What's the correct way to set up Django translation?

Please set translated string in django.po and then use python manage.py compilemessages

for e.g 

#: path/to/python/module.py:23
msgid "Welcome to my site."
msgstr "put appropriate translated string here"

Suggestion-: You can use django-rosetta package to add translated string from UI interface. It is easy to add T-string from django-admin. https://github.com/mbi/django-rosetta

You need to enable the LocaleMiddleware in your settings, to tell Django to do language detection based on the browser-settings. Changing your language preferences effectly sets the Accept-Language header. You might need to check in an incognito window, because other means of language detection have a higher priority, such as the user’s session and the django_language cookie.

Check the cookies and the session — according to How Django Discovers Language Preference, the process is this:

1. language prefix in the URL, when using i18n_patterns in URLconf
2. _language key in the current user’s session
3. django_language cookie (or as specified by settings.LANGUAGE_COOKIE_NAME)
4. Accept-Language HTTP header (this is what your browser setting sends)
5. settings.LANGUAGE_CODE

Since your browser settings are set to prefer ‘de’, I suspect the LocaleMiddleware must decide otherwise in one of the previous steps 1. – 3.

In my case, I used en-gb as the parameter to run

django-admin.py makemessages -l en-gb

Instead, it should be en_GB.

django-admin.py makemessages -l en_GB

For example below, you can translate English to French.

First, create locale folder just under django-project as shown below. *I use Django 4.2.1 and you can see my answer explaining how to set templates:

django-project
 |-core
 |  |-settings.py
 |  └-urls.py
 |-my_app1
 |  |-views.py
 |  |-urls.py
 |  |-models.py
 |  |_admin.py
 |  └-apps.py
 |-my_app2
 |-templates
 |  └-index.html  
 └-locale # Here

Then, set core/settings.py as shown below. *LocaleMiddleware must be between SessionMiddleware and CommonMiddleware. 'en-us' is set to LANGUAGE_CODE by default in core/settings.py:

# "core/settings.py"

MIDDLEWARE = [
    ...
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.locale.LocaleMiddleware', # Here
    'django.middleware.common.CommonMiddleware',
    ...
]

LANGUAGE_CODE = 'en-us'

TIME_ZONE = 'UTC'

USE_I18N = True

USE_TZ = True

from django.utils.translation import gettext_lazy as _

LANGUAGES = ( # Here
    ('en', _('English')),
    ('fr', _('French'))
)

And, Hello and World are translated and outputted on console and index.html is rendered in test() in my_app1/views.py as shown below:

# "my_app1/views.py"

from django.shortcuts import render
from django.utils.translation import gettext as _

def test(request):
    print(_("Hello"), _("World")) # Here
    return render(request, 'index.html')

And, test() path is set to urlpatterns in my_app1/urls.py as shown below:

# "my_app1/urls.py"

from django.urls import path
from . import views

app_name = "my_app1"

urlpatterns = [
    path('', views.test, name="test") # Here
]

And, admin and my_app1 paths are set to urlpatterns with i18n_patterns() in core/urls.py as shown below. *You can see my question and my answer explaining prefix_default_language=False with i18n_patterns():

# "core/urls.py"

from django.contrib import admin
from django.urls import path, include
from django.conf.urls.i18n import i18n_patterns

urlpatterns = i18n_patterns(
    path('admin/', admin.site.urls), # Here
    path('my_app1/', include('my_app1.urls')) # Here
)

And, 3 tags are set in templates/index.py as shown below. *For the translation in Django Templates, {% load i18n %} is needed and {% translate %} or {% trans %} can translate:

# "templates/index.py"

{% load i18n %}

{% translate "Hello" %} {% trans "World" %}

And, name field and person model are translated in my_app1/models.py as shown below:

# "my_app1/models.py"

from django.db import models
from django.utils.translation import gettext_lazy as _

class Person(models.Model):
    first_name = models.CharField(
        max_length=20, verbose_name=_("first name") # Here
    )
    last_name = models.CharField(
        max_length=20, verbose_name=_("last name") # Here
    )

    class Meta:
        verbose_name = _('person') # Here
        verbose_name_plural = _('persons') # Here

And, this is my_app1/admin.py below:

# "my_app1/admin.py"

from django.contrib import admin
from .models import Person

@admin.register(Person)
class PersonAdmin(admin.ModelAdmin):
    pass

And, my_app1 is translated in my_app1/apps.py as shown below:

# "my_app1/apps.py"

from django.apps import AppConfig
from django.utils.translation import gettext_lazy as _

class MyApp1Config(AppConfig):
    default_auto_field = 'django.db.models.BigAutoField'
    name = 'my_app1'
    verbose_name = _('my_app1') # Here

Now, run the command below. *You can see my answer explaining the command below:

django-admin makemessages -l fr

Then, django.po is created in locale/fr/LC_MESSAGES/ as shown below:

django-project
 |-core
 |  |-settings.py
 |  └-urls.py
 |-my_app1
 |  |-views.py
 |  |-urls.py
 |  |-models.py
 |  |_admin.py
 |  └-apps.py
 |-my_app2
 |-templates
 |  └-index.html  
 └-locale
    └-fr
       └-LC_MESSAGES
          └-django.po # Here

Then, add Bonjour, Monde, Anglais and Français to each msgstr "" respectively in locale/fr/LC_MESSAGES/django.po as shown below:

# "locale/fr/LC_MESSAGES/django.po"

...

#: .coresettings.py:140
msgid "English"
msgstr "Anglais" # Here

#: .coresettings.py:141
msgid "French"
msgstr "Français" # Here

#: .my_app1apps.py:7
msgid "my_app1"
msgstr "mon_app1" # Here

#: .my_app1models.py:6
msgid "first name"
msgstr "prénom"

#: .my_app1models.py:7
msgid "last name"
msgstr "nom de famille"

#: .my_app1models.py:13
msgid "person"
msgstr "personne"

#: .my_app1models.py:14
msgid "persons"
msgstr "personnes"

#: .my_app1views.py:5 .templatesindex.html:3
msgid "Hello"
msgstr "Bonjour" # Here

#: .my_app1views.py:5 .templatesindex.html:3
msgid "World"
msgstr "Monde" # Here

...

Then, run the command below to compile django.po to django.mo. *You can see my answer explaining the command below:

django-admin compilemessages

Then, django.po is compiled to django.mo in locale/fr/LC_MESSAGES/ as shown below:

django-project
 |-core
 |  |-settings.py
 |  └-urls.py
 |-my_app1
 |  |-views.py
 |  |-urls.py
 |  |-models.py
 |  |_admin.py
 |  └-apps.py
 |-my_app2
 |-templates
 |  └-index.html
 └-locale
    └-fr
       └-LC_MESSAGES
          |-django.po
          └-django.mo # Here

Now, http://localhost:8000/en/my_app1/ can show Hello World as shown below:

And, Hello World below is outputted on console:

Hello World

And, http://localhost:8000/fr/my_app1/ can show Bonjour Monde as shown below:

And, Bonjour Monde below is outputted on console:

Bonjour Monde

And, http://localhost:8000/en/admin/my_app1/person/add/ can show the English version of Django Admin as shown below:

And, http://localhost:8000/fr/admin/my_app1/person/add/ can show the French version of Django Admin as shown below: