Deactivate translations instead of forcing 'en-us' in management commands

[Claude Paroz]

This has been mentioned in #16284, which aims to depart from defaulting to 'en' for JS i18n.

This ticket is concentrating on a similar move for management commands.

[Claude Paroz]

​https://github.com/django/django/pull/3838

[Claude Paroz <claude@…>]

In f7c287fca9c9e6370cc88d1457d3ed9466703687:

Fixed #24073 -- Deactivated translations when leave_locale_alone is False

Thanks Tim Graham and Markus Holtermann for the reviews.

[Markus Holtermann]

This causes a regression with strings marked for lazy translation.

If you check out ​https://github.com/MarkusH/django-ticket-triage/commit/54fddd35795f71fea34cf4a166a271f9277e3d19 and run migrate twice, the second time Django will complain that there are changes not reflected by the migrations.

Some of ​those changes are AlterField operations:

ipdb> changes['conference'][0].operations
[<AlterField  field=<django.db.models.fields.CharField: name>, preserve_default=True, model_name='audiencelevel', name='name'>, <AlterField  field=<django.db.models.fields.CharField: name>, preserve_default=True, model_name='location', name='name'>, <AlterField  field=<django.db.models.fields.CharField: name>, preserve_default=True, model_name='section', name='name'>, <AlterField  field=<django.db.models.fields.CharField: name>, preserve_default=True, model_name='sessionkind', name='name'>, <AlterField  field=<django.db.models.fields.CharField: name>, preserve_default=True, model_name='track', name='name'>]

Inspecting generate_altered_fields() in the migration autodetector yield

> /home/markus/Coding/django/django/db/migrations/autodetector.py(853)generate_altered_fields()
    852                 import ipdb; ipdb.set_trace()  # TODO: debugger
--> 853                 if (not isinstance(old_field, models.ManyToManyField) and
    854                         not isinstance(new_field, models.ManyToManyField)):

ipdb> old_field_dec
('django.db.models.PositiveSmallIntegerField', [], {'verbose_name': 'action flag'})
ipdb> new_field_dec
('django.db.models.PositiveSmallIntegerField', [], {'verbose_name': <django.utils.functional.lazy.<locals>.__proxy__ object at 0x7f044e1e58d0>})

git bisect pin-points the change to f7c287fca9c9e6370cc88d1457d3ed9466703687

[Claude Paroz]

At least I've understood what's happening. As migrate is calling another management command (loaddata), that last command is restoring the default language code at exit, hence canceling the deactivate_all call from the base command. And then of course, the autodetector is fooled by the translated verbose_name.

Semantically, I think that the root cause is get_language returning settings.LANGUAGE_CODE when translations are deactivated. I'll see if we can safely fix that.

[Claude Paroz]

PR: ​https://github.com/django/django/pull/3856

[Claude Paroz <claude@…>]

In 543df07720181fe23737ba14f1a261ff6f37f49c:

Fixed #24073 -- Returned None for get_language when translations are deactivated

This fixes a regression caused by f7c287fca9. Thanks Markus Holtermann
for identifying the regression.

[Tim Graham <timograham@…>]

In b9cec9fa:

Fixed #29017 -- Updated BaseCommand.leave_locale_alone doc per refs #24073.

[Tim Graham <timograham@…>]

In 3f951b1:

[2.0.x] Fixed #29017 -- Updated BaseCommand.leave_locale_alone doc per refs #24073.

Backport of b9cec9fa1fc50207ab68a59853c851a945c5db5e from master

[Tim Graham <timograham@…>]

In ced0b1e:

[1.11.x] Fixed #29017 -- Updated BaseCommand.leave_locale_alone doc per refs #24073.

Backport of b9cec9fa1fc50207ab68a59853c851a945c5db5e from master