How to override the django admin translation?

I'm providing an answer, even though @hedgie mostly answered their own question. I'll add a bit of context and description of what's happening. This answer is still applicable as of Django 3.0.

Just as you can override a Django-provided admin template by duplicating the template's name and directory structure within our own project, you can override Django-provided admin translations by duplicating a .po file's name and directory structure within our project.

Django's admin translations live in django/contrib/admin/locale/ and are organized by language in directories named [language code]/LC_MESSAGES/. These individual language directories contain two .po files, django.po and djangojs.po, and their respective compiled .mo files. You will be overriding the .po files, and compiling our own .mo files.

The first thing you have to do is enable translations in settings, and tell Django where you store our translation files.

settings.py

import osBASE_DIR = os.path.dirname(os.path.dirname(__file__))# ...LANGUAGE_CODE = 'nl-NL'USE_I18N = TrueUSE_L10N = TrueLOCALE_PATHS = (os.path.join(BASE_DIR, "locale"),)  # our custom translations will go here

Note that although the directory Django uses is nl, the full language identifier for Dutch in the Netherlands is nl-NL. You can find a full list of identifiers organized by country here.

Next, you'll mimic Django's directory structure and create two files in a new directory:

my_project/locale/nl/LC_MESSAGES/django.po

my_project/locale/nl/LC_MESSAGES/djangojs.po

Note that this path must also match what you provided in settings.py.

Copy and paste the contents of Django's translation files. You can now edit the translations for whichever strings you like. For example:

django.po

msgid "Are you sure?"--- msgstr "Weet u het zeker?"+++ msgstr "Weet u het zeker?!"

Now you need to compile the messages with:

python manage.py compilemessages

This command compiles your .po files into .mo files, which Django will use to translate any matching gettext calls. You should now see your custom translations in the admin interface.