Support for converting datetime locale based on Django

[slashmili]

The idea is to let django_jalali uses Django locale rather than system level locale when printing dates.

Given these settings

....
# Internationalization
# https://docs.djangoproject.com/en/1.10/topics/i18n/

LANGUAGE_CODE = 'fa-ir'

TIME_ZONE = 'Asia/Tehran'

USE_I18N = True

USE_L10N = True

USE_TZ = True


MIDDLEWARE = [
    'django.middleware.cache.UpdateCacheMiddleware',
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.locale.LocaleMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
    'reversion.middleware.RevisionMiddleware',
    'django.middleware.cache.FetchFromCacheMiddleware',
]
....

And this change:

diff --git a/django_jalali/templatetags/jformat.py b/django_jalali/templatetags/jformat.py
index fe265e6..3524ad8 100644
--- a/django_jalali/templatetags/jformat.py
+++ b/django_jalali/templatetags/jformat.py
@@ -1,5 +1,6 @@
 from distutils.version import StrictVersion
 import django
+from django.utils.translation import to_locale, get_language
 import sys
 from datetime import datetime, date
 import jdatetime
@@ -16,6 +17,7 @@ register = Library()
 @register.filter(expects_localtime=True, is_safe=False)
 def jformat(value, arg=None):
     """Formats a date or time according to the given format."""
+    jdatetime.set_locale(to_locale(get_language()))
     if value in (None, ''):
         return ''
     if arg is None:

It does work in some cases. However if the user has messed up locale settings in browser or user is from outside of Iran with different browser settings, Django get_language function returns en or de or any other locale and the date is going to be printed in English.

cc @Alireza2n @farzadghanei

[farzadghanei]

It's a good idea, provides a sensible default value for locale based on the request. I like detecting best case defaults automatically, with enough room for configurations.

Maybe we can provide a way for the Django app (via django-jalali settings) to specify the priority of places to look for the default locale, giving the app more control over such behavior. The options to read locale from could be:

• request headers (browser settings)
• request params (app specific query param name to chose the locale for multi lang apps, like lang or locale etc.)
• Django settings (default static locale for the app)
• system locale (as is already picked by jdatetime by default)

[slashmili]

There is already a complicated logic for django to find the closest locale for user https://github.com/django/django/blob/master/django/middleware/locale.py

it supports reading the language/locale from :

• Headers
• path in URL

So I guess we can only have an option to get locale from what this middleware has set or get the locale from LANGUAGE_CODE in settings.py

[farzadghanei]

Yeah seems good, we won't need to do what's already done plus it'll be a better integration. So the request carries the proper language code. There is also django.utils.translation.get_language_from_request().

We can provide a way for the app to specify the order (priority) to pick the locale from request (using any of the above methods), or an explicit settings (so the app has an option to enforce the locale).