[3.1.x] Fixed #31570 -- Corrected translation loading for apps providing territorial language variants with different plural equations.

Regression in e3e48b00127c09eafe6439d980a82fc5c591b673.

Thanks to Shai Berger for report, reproduce and suggested fix.

Backport of dd1ca50b096bf0351819aabc862e91a9797ddaca from master

16 files changed, 176 insertions, 3 deletions

diff --git a/django/utils/translation/trans_real.py b/django/utils/translation/trans_real.py
index eed4705f6e..8042f6fdc4 100644
--- a/django/utils/translation/trans_real.py
+++ b/django/utils/translation/trans_real.py
@@ -96,7 +96,7 @@ class TranslationCatalog:
                 cat.update(trans._catalog)
                 break
         else:
-            self._catalogs.insert(0, trans._catalog)
+            self._catalogs.insert(0, trans._catalog.copy())
             self._plurals.insert(0, trans.plural)
 
     def get(self, key, default=None):
diff --git a/docs/releases/2.2.13.txt b/docs/releases/2.2.13.txt
index 450f7acdbf..cc0739e646 100644
--- a/docs/releases/2.2.13.txt
+++ b/docs/releases/2.2.13.txt
@@ -4,9 +4,12 @@ Django 2.2.13 release notes
 
 *Expected June 3, 2020*
 
-Django 2.2.13 fixes two security issues and a bug in 2.2.12.
+Django 2.2.13 fixes two security issues and a regression in 2.2.12.
 
 Bugfixes
 ========
 
-* ...
+* Fixed a regression in Django 2.2.12 that affected translation loading for
+  apps providing translations for territorial language variants as well as a
+  generic language, where the project has different plural equations for the
+  language (:ticket:`31570`).
diff --git a/docs/releases/3.0.7.txt b/docs/releases/3.0.7.txt
index c7bc3730fd..b38a8d8059 100644
--- a/docs/releases/3.0.7.txt
+++ b/docs/releases/3.0.7.txt
@@ -25,3 +25,8 @@ Bugfixes
 
 * Fixed a regression in Django 3.0 where all resolved ``Subquery()``
   expressions were considered equal (:ticket:`31607`).
+
+* Fixed a regression in Django 3.0.5 that affected translation loading for apps
+  providing translations for territorial language variants as well as a generic
+  language, where the project has different plural equations for the language
+  (:ticket:`31570`).
diff --git a/tests/i18n/loading/en/LC_MESSAGES/django.mo b/tests/i18n/loading/en/LC_MESSAGES/django.mo
new file mode 100644
index 0000000000..f666550adb
--- /dev/null
+++ b/tests/i18n/loading/en/LC_MESSAGES/django.mo
diff --git a/tests/i18n/loading/en/LC_MESSAGES/django.po b/tests/i18n/loading/en/LC_MESSAGES/django.po
new file mode 100644
index 0000000000..d43d83e34a
--- /dev/null
+++ b/tests/i18n/loading/en/LC_MESSAGES/django.po
@@ -0,0 +1,23 @@
+# SOME DESCRIPTIVE TITLE.
+# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
+# This file is distributed under the same license as the PACKAGE package.
+# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
+#
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: PACKAGE VERSION\n"
+"Report-Msgid-Bugs-To: \n"
+"POT-Creation-Date: 2020-05-13 08:42+0000\n"
+"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
+"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
+"Language-Team: LANGUAGE <LL@li.org>\n"
+"Language: \n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+#: trans/tests.py:16
+msgid "local country person"
+msgstr "local country person"
diff --git a/tests/i18n/loading/en_AU/LC_MESSAGES/django.mo b/tests/i18n/loading/en_AU/LC_MESSAGES/django.mo
new file mode 100644
index 0000000000..98b016bc6c
--- /dev/null
+++ b/tests/i18n/loading/en_AU/LC_MESSAGES/django.mo
diff --git a/tests/i18n/loading/en_AU/LC_MESSAGES/django.po b/tests/i18n/loading/en_AU/LC_MESSAGES/django.po
new file mode 100644
index 0000000000..ec21ac899d
--- /dev/null
+++ b/tests/i18n/loading/en_AU/LC_MESSAGES/django.po
@@ -0,0 +1,23 @@
+# SOME DESCRIPTIVE TITLE.
+# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
+# This file is distributed under the same license as the PACKAGE package.
+# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
+#
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: PACKAGE VERSION\n"
+"Report-Msgid-Bugs-To: \n"
+"POT-Creation-Date: 2020-05-13 08:42+0000\n"
+"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
+"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
+"Language-Team: LANGUAGE <LL@li.org>\n"
+"Language: \n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+#: trans/tests.py:16
+msgid "local country person"
+msgstr "aussie"
diff --git a/tests/i18n/loading/en_CA/LC_MESSAGES/django.mo b/tests/i18n/loading/en_CA/LC_MESSAGES/django.mo
new file mode 100644
index 0000000000..4d6da00f65
--- /dev/null
+++ b/tests/i18n/loading/en_CA/LC_MESSAGES/django.mo
diff --git a/tests/i18n/loading/en_CA/LC_MESSAGES/django.po b/tests/i18n/loading/en_CA/LC_MESSAGES/django.po
new file mode 100644
index 0000000000..06e52a4c55
--- /dev/null
+++ b/tests/i18n/loading/en_CA/LC_MESSAGES/django.po
@@ -0,0 +1,22 @@
+# SOME DESCRIPTIVE TITLE.
+# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
+# This file is distributed under the same license as the PACKAGE package.
+# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
+#
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: PACKAGE VERSION\n"
+"Report-Msgid-Bugs-To: \n"
+"POT-Creation-Date: 2020-05-13 08:42+0000\n"
+"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
+"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
+"Language-Team: LANGUAGE <LL@li.org>\n"
+"Language: \n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+
+#: trans/tests.py:16
+msgid "local country person"
+msgstr "canuck"
diff --git a/tests/i18n/loading/en_NZ/LC_MESSAGES/django.mo b/tests/i18n/loading/en_NZ/LC_MESSAGES/django.mo
new file mode 100644
index 0000000000..f71850a5b1
--- /dev/null
+++ b/tests/i18n/loading/en_NZ/LC_MESSAGES/django.mo
diff --git a/tests/i18n/loading/en_NZ/LC_MESSAGES/django.po b/tests/i18n/loading/en_NZ/LC_MESSAGES/django.po
new file mode 100644
index 0000000000..41b7499291
--- /dev/null
+++ b/tests/i18n/loading/en_NZ/LC_MESSAGES/django.po
@@ -0,0 +1,22 @@
+# SOME DESCRIPTIVE TITLE.
+# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
+# This file is distributed under the same license as the PACKAGE package.
+# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
+#
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: PACKAGE VERSION\n"
+"Report-Msgid-Bugs-To: \n"
+"POT-Creation-Date: 2020-05-13 08:42+0000\n"
+"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
+"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
+"Language-Team: LANGUAGE <LL@li.org>\n"
+"Language: \n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+
+#: trans/tests.py:16
+msgid "local country person"
+msgstr "kiwi"
diff --git a/tests/i18n/loading_app/__init__.py b/tests/i18n/loading_app/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/i18n/loading_app/__init__.py
diff --git a/tests/i18n/loading_app/apps.py b/tests/i18n/loading_app/apps.py
new file mode 100644
index 0000000000..b4cdece232
--- /dev/null
+++ b/tests/i18n/loading_app/apps.py
@@ -0,0 +1,5 @@
+from django.apps import AppConfig
+
+
+class LoadingAppConfig(AppConfig):
+    name = 'loading_app'
diff --git a/tests/i18n/loading_app/locale/en/LC_MESSAGES/django.mo b/tests/i18n/loading_app/locale/en/LC_MESSAGES/django.mo
new file mode 100644
index 0000000000..71cbdf3e9d
--- /dev/null
+++ b/tests/i18n/loading_app/locale/en/LC_MESSAGES/django.mo
diff --git a/tests/i18n/loading_app/locale/en/LC_MESSAGES/django.po b/tests/i18n/loading_app/locale/en/LC_MESSAGES/django.po
new file mode 100644
index 0000000000..e1422f19da
--- /dev/null
+++ b/tests/i18n/loading_app/locale/en/LC_MESSAGES/django.po
@@ -0,0 +1,25 @@
+# SOME DESCRIPTIVE TITLE.
+# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
+# This file is distributed under the same license as the PACKAGE package.
+# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
+#
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: PACKAGE VERSION\n"
+"Report-Msgid-Bugs-To: \n"
+"POT-Creation-Date: 2020-05-13 11:39+0300\n"
+"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
+"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
+"Language-Team: LANGUAGE <LL@li.org>\n"
+"Language: \n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+#: apps.py:8
+msgid ""
+"An app with its own translation files, with one for 'en' but not the "
+"regional dialects of English"
+msgstr ""
diff --git a/tests/i18n/tests.py b/tests/i18n/tests.py
index 8f07c14247..feca7b856f 100644
--- a/tests/i18n/tests.py
+++ b/tests/i18n/tests.py
@@ -384,6 +384,51 @@ class TranslationTests(SimpleTestCase):
             self.assertIs(get_language_bidi(), True)
 
 
+class TranslationLoadingTests(SimpleTestCase):
+    def setUp(self):
+        """Clear translation state."""
+        self._old_language = get_language()
+        self._old_translations = trans_real._translations
+        deactivate()
+        trans_real._translations = {}
+
+    def tearDown(self):
+        trans_real._translations = self._old_translations
+        activate(self._old_language)
+
+    @override_settings(
+        USE_I18N=True,
+        LANGUAGE_CODE='en',
+        LANGUAGES=[
+            ('en', 'English'),
+            ('en-ca', 'English (Canada)'),
+            ('en-nz', 'English (New Zealand)'),
+            ('en-au', 'English (Australia)'),
+        ],
+        LOCALE_PATHS=[os.path.join(here, 'loading')],
+        INSTALLED_APPS=['i18n.loading_app'],
+    )
+    def test_translation_loading(self):
+        """
+        "loading_app" does not have translations for all languages provided by
+        "loading". Catalogs are merged correctly.
+        """
+        tests = [
+            ('en', 'local country person'),
+            ('en_AU', 'aussie'),
+            ('en_NZ', 'kiwi'),
+            ('en_CA', 'canuck'),
+        ]
+        # Load all relevant translations.
+        for language, _ in tests:
+            activate(language)
+        # Catalogs are merged correctly.
+        for language, nickname in tests:
+            with self.subTest(language=language):
+                activate(language)
+                self.assertEqual(gettext('local country person'), nickname)
+
+
 class TranslationThreadSafetyTests(SimpleTestCase):
 
     def setUp(self):