Fixed #21113 -- Made LogEntry.change_message language independent

Thanks Tim Graham for the review.

docs/ref/contrib/admin/index.txt

@@ -2823,7 +2823,18 @@ password box.
 .. attribute:: LogEntry.change_message
 
     The detailed description of the modification. In the case of an edit, for
-    example, the message contains a list of the edited fields.
+    example, the message contains a list of the edited fields. The Django admin
+    site formats this content as a JSON structure, so that
+    :meth:`get_change_message` can recompose a message translated in the current
+    user language. Custom code might set this as a plain string though. You are
+    advised to use the :meth:`get_change_message` method to retrieve this value
+    instead of accessing it directly.
+
+    .. versionchanged:: 1.10
+
+        Previously, this attribute was always a plain string. It is
+        now JSON-structured so that the message can be translated in the current
+        user language. Old messages are untouched.
 
 ``LogEntry`` methods
 --------------------
@@ -2832,6 +2843,14 @@ password box.
 
     A shortcut that returns the referenced object.
 
+.. method:: LogEntry.get_change_message()
+
+    .. versionadded:: 1.10
+
+    Formats and translates :attr:`change_message` into the current user
+    language. Messages created before Django 1.10 will always be displayed in
+    the language in which they were logged.
+
 .. currentmodule:: django.contrib.admin
 
 .. _admin-reverse-urls:

docs/releases/1.10.txt

@@ -51,6 +51,11 @@ Minor features
   model's changelist will now be rendered (without the add button, of course).
   This makes it easier to add custom tools in this case.
 
+* The :class:`~django.contrib.admin.models.LogEntry` model now stores change
+  messages in a JSON structure so that the message can be dynamically translated
+  using the current active language. A new ``LogEntry.get_change_message()``
+  method is now the preferred way of retrieving the change message.
+
 :mod:`django.contrib.admindocs`
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -417,6 +422,10 @@ Miscellaneous
 * :djadmin:`loaddata` now raises a ``CommandError`` instead of showing a
   warning when the specified fixture file is not found.
 
+* Instead of directly accessing the ``LogEntry.change_message`` attribute, it's
+  now better to call the ``LogEntry.get_change_message()`` method which will
+  provide the message in the current language.
+
 .. _deprecated-features-1.10:
 
 Features deprecated in 1.10