Fixed #32873 -- Deprecated settings.USE_L10N.

Co-authored-by: Mariusz Felisiak <felisiak.mariusz@gmail.com>

5 files changed, 72 insertions, 10 deletions

diff --git a/django/conf/__init__.py b/django/conf/__init__.py
index 628b1f7e4d..f8018f723b 100644
--- a/django/conf/__init__.py
+++ b/django/conf/__init__.py
@@ -9,9 +9,11 @@ for a list of all possible variables.
 import importlib
 import os
 import time
+import traceback
 import warnings
 from pathlib import Path
 
+import django
 from django.conf import global_settings
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.deprecation import RemovedInDjango50Warning
@@ -19,6 +21,12 @@ from django.utils.functional import LazyObject, empty
 
 ENVIRONMENT_VARIABLE = "DJANGO_SETTINGS_MODULE"
 
+USE_L10N_DEPRECATED_MSG = (
+    'The USE_L10N setting is deprecated. Starting with Django 5.0, localized '
+    'formatting of data will always be enabled. For example Django will '
+    'display numbers and dates using the format of the current locale.'
+)
+
 
 class SettingsReference(str):
     """
@@ -129,6 +137,27 @@ class LazySettings(LazyObject):
         """Return True if the settings have already been configured."""
         return self._wrapped is not empty
 
+    @property
+    def USE_L10N(self):
+        stack = traceback.extract_stack()
+        # Show a warning if the setting is used outside of Django.
+        # Stack index: -1 this line, -2 the caller.
+        filename, _, _, _ = stack[-2]
+        if not filename.startswith(os.path.dirname(django.__file__)):
+            warnings.warn(
+                USE_L10N_DEPRECATED_MSG,
+                RemovedInDjango50Warning,
+                stacklevel=2,
+            )
+        return self.__getattr__('USE_L10N')
+
+    # RemovedInDjango50Warning.
+    @property
+    def _USE_L10N_INTERNAL(self):
+        # Special hook to avoid checking a traceback in internal use on hot
+        # paths.
+        return self.__getattr__('USE_L10N')
+
 
 class Settings:
     def __init__(self, settings_module):
@@ -179,6 +208,9 @@ class Settings:
             os.environ['TZ'] = self.TIME_ZONE
             time.tzset()
 
+        if self.is_overridden('USE_L10N'):
+            warnings.warn(USE_L10N_DEPRECATED_MSG, RemovedInDjango50Warning)
+
     def is_overridden(self, setting):
         return setting in self._explicit_settings
 
@@ -210,6 +242,8 @@ class UserSettingsHolder:
 
     def __setattr__(self, name, value):
         self._deleted.discard(name)
+        if name == 'USE_L10N':
+            warnings.warn(USE_L10N_DEPRECATED_MSG, RemovedInDjango50Warning)
         super().__setattr__(name, value)
 
     def __delattr__(self, name):
diff --git a/django/conf/global_settings.py b/django/conf/global_settings.py
index b9541d81b5..ab69316314 100644
--- a/django/conf/global_settings.py
+++ b/django/conf/global_settings.py
@@ -167,7 +167,7 @@ LANGUAGE_COOKIE_SAMESITE = None
 
 # If you set this to True, Django will format dates, numbers and calendars
 # according to user current locale.
-USE_L10N = False
+USE_L10N = True
 
 # Not-necessarily-technical managers of the site. They get broken link
 # notifications and other various emails.
diff --git a/django/conf/locale/en/formats.py b/django/conf/locale/en/formats.py
index ccace3d2b3..f5af6509c6 100644
--- a/django/conf/locale/en/formats.py
+++ b/django/conf/locale/en/formats.py
@@ -2,24 +2,36 @@
 #
 # The *_FORMAT strings use the Django date format syntax,
 # see https://docs.djangoproject.com/en/dev/ref/templates/builtins/#date
+
+# Formatting for date objects.
 DATE_FORMAT = 'N j, Y'
+# Formatting for time objects.
 TIME_FORMAT = 'P'
+# Formatting for datetime objects.
 DATETIME_FORMAT = 'N j, Y, P'
+# Formatting for date objects when only the year and month are relevant.
 YEAR_MONTH_FORMAT = 'F Y'
+# Formatting for date objects when only the month and day are relevant.
 MONTH_DAY_FORMAT = 'F j'
+# Short formatting for date objects.
 SHORT_DATE_FORMAT = 'm/d/Y'
+# Short formatting for datetime objects.
 SHORT_DATETIME_FORMAT = 'm/d/Y P'
-FIRST_DAY_OF_WEEK = 0  # Sunday
+# First day of week, to be used on calendars.
+# 0 means Sunday, 1 means Monday...
+FIRST_DAY_OF_WEEK = 0
 
+# Formats to be used when parsing dates from input boxes, in order.
 # The *_INPUT_FORMATS strings use the Python strftime format syntax,
 # see https://docs.python.org/library/datetime.html#strftime-strptime-behavior
+# Note that these format strings are different from the ones to display dates.
 # Kept ISO formats as they are in first position
 DATE_INPUT_FORMATS = [
     '%Y-%m-%d', '%m/%d/%Y', '%m/%d/%y',  # '2006-10-25', '10/25/2006', '10/25/06'
-    # '%b %d %Y', '%b %d, %Y',            # 'Oct 25 2006', 'Oct 25, 2006'
-    # '%d %b %Y', '%d %b, %Y',            # '25 Oct 2006', '25 Oct, 2006'
-    # '%B %d %Y', '%B %d, %Y',            # 'October 25 2006', 'October 25, 2006'
-    # '%d %B %Y', '%d %B, %Y',            # '25 October 2006', '25 October, 2006'
+    '%b %d %Y', '%b %d, %Y',             # 'Oct 25 2006', 'Oct 25, 2006'
+    '%d %b %Y', '%d %b, %Y',             # '25 Oct 2006', '25 Oct, 2006'
+    '%B %d %Y', '%B %d, %Y',             # 'October 25 2006', 'October 25, 2006'
+    '%d %B %Y', '%d %B, %Y',             # '25 October 2006', '25 October, 2006'
 ]
 DATETIME_INPUT_FORMATS = [
     '%Y-%m-%d %H:%M:%S',     # '2006-10-25 14:30:59'
@@ -32,6 +44,16 @@ DATETIME_INPUT_FORMATS = [
     '%m/%d/%y %H:%M:%S.%f',  # '10/25/06 14:30:59.000200'
     '%m/%d/%y %H:%M',        # '10/25/06 14:30'
 ]
+TIME_INPUT_FORMATS = [
+    '%H:%M:%S',     # '14:30:59'
+    '%H:%M:%S.%f',  # '14:30:59.000200'
+    '%H:%M',        # '14:30'
+]
+
+# Decimal separator symbol.
 DECIMAL_SEPARATOR = '.'
+# Thousand separator symbol.
 THOUSAND_SEPARATOR = ','
+# Number of digits that will be together, when splitting them by
+# THOUSAND_SEPARATOR. 0 means no grouping, 3 means splitting by thousands.
 NUMBER_GROUPING = 3
diff --git a/django/conf/project_template/project_name/settings.py-tpl b/django/conf/project_template/project_name/settings.py-tpl
index e949752df4..3b6caab333 100644
--- a/django/conf/project_template/project_name/settings.py-tpl
+++ b/django/conf/project_template/project_name/settings.py-tpl
@@ -109,8 +109,6 @@ TIME_ZONE = 'UTC'
 
 USE_I18N = True
 
-USE_L10N = True
-
 USE_TZ = True
 
 
diff --git a/django/utils/formats.py b/django/utils/formats.py
index cffbb34398..781d334a8e 100644
--- a/django/utils/formats.py
+++ b/django/utils/formats.py
@@ -104,7 +104,11 @@ def get_format(format_type, lang=None, use_l10n=None):
     If use_l10n is provided and is not None, it forces the value to
     be localized (or not), overriding the value of settings.USE_L10N.
     """
-    use_l10n = use_l10n or (use_l10n is None and settings.USE_L10N)
+    use_l10n = use_l10n or (use_l10n is None and (
+        settings._USE_L10N_INTERNAL
+        if hasattr(settings, '_USE_L10N_INTERNAL')
+        else settings.USE_L10N
+    ))
     if use_l10n and lang is None:
         lang = get_language()
     cache_key = (format_type, lang)
@@ -168,7 +172,11 @@ def number_format(value, decimal_pos=None, use_l10n=None, force_grouping=False):
     If use_l10n is provided and is not None, it forces the value to
     be localized (or not), overriding the value of settings.USE_L10N.
     """
-    use_l10n = use_l10n or (use_l10n is None and settings.USE_L10N)
+    use_l10n = use_l10n or (use_l10n is None and (
+        settings._USE_L10N_INTERNAL
+        if hasattr(settings, '_USE_L10N_INTERNAL')
+        else settings.USE_L10N
+    ))
     lang = get_language() if use_l10n else None
     return numberformat.format(
         value,