Do not use local override for language settings: always sync.

chrome/common/pref_names.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/common/pref_names.h"
 
 namespace prefs {
 
 // *************** PROFILE PREFS ***************
 // These are attached to the user profile
@@ skipping 28 matching lines @@
 // The URLs to restore on startup or when the home button is pressed. The URLs
 // are only restored on startup if kRestoreOnStartup is 4.
 const char kURLsToRestoreOnStartup[] = "session.urls_to_restore_on_startup";
 
 // The application locale.
 // For OS_CHROMEOS we maintain kApplicationLocale property in both local state
 // and user's profile.  Global property determines locale of login screen,
 // while user's profile determines his personal locale preference.
 const char kApplicationLocale[] = "intl.app_locale";
 #if defined(OS_CHROMEOS)
-// Non-syncable item.  Used to detect locale change.
-// Used for two-step initialization of locale in ChromeOS
-// because synchronization of kApplicationLocale is not instant.
-const char kApplicationLocaleBackup[] = "intl.app_locale_backup";
-// Non-syncable item.
-// Used to locally override synchronized kApplicationLocale preference.
-const char kApplicationLocaleOverride[] = "intl.app_locale_override";
 // Locale accepted by user.  Non-syncable.
 // Used to determine whether we need to show Locale Change notification.
 const char kApplicationLocaleAccepted[] = "intl.app_locale_accepted";
+// Non-syncable item.
+// It is used in two distinct ways.
+// (1) Used for two-step initialization of locale in ChromeOS
+//     because synchronization of kApplicationLocale is not instant.
+// (2) Used to detect locale change.  Locale change is detected by
+//     LocaleChangeGuard in case values of kApplicationLocaleBackup and
+//     kApplicationLocale are both non-empty and differ.
+// Following is a table showing how state of those prefs may change upon
+// common real-life use cases:
+//                                  AppLocale Backup Accepted
+// Initial login                       -        A       -
+// Sync                                B        A       -
+// Accept (B)                          B        B       B
+// -----------------------------------------------------------
+// Initial login                       -        A       -
+// No sync and second login            A        A       -
+// Change options                      B        B       -
+// -----------------------------------------------------------
+// Initial login                       -        A       -
+// Sync                                A        A       -
+// Locale changed on login screen      A        C       -

[Nikita (slow), 2011/01/25 16:04:44]

As we discussed locale change in settings behaves differently i.e. always clears
"accepted" pref.

Is it possible to eliminate "accepted" preference since we always show that
notification when sync language is different?

+// Accept (A)                          A        A       A
+// -----------------------------------------------------------
+// Initial login                       -        A       -
+// Sync                                B        A       -
+// Revert                              A        A       -
+const char kApplicationLocaleBackup[] = "intl.app_locale_backup";
 #endif
 
 // The default character encoding to assume for a web page in the
 // absence of MIME charset specification
 const char kDefaultCharset[] = "intl.charset_default";
 
 // The value to use for Accept-Languages HTTP header when making an HTTP
 // request.
 const char kAcceptLanguages[] = "intl.accept_languages";
 
@@ skipping 1131 matching lines @@
 const char kManagedDefaultPluginsSetting[] =
     "profile.managed_default_content_settings.plugins";
 const char kManagedDefaultPopupsSetting[] =
     "profile.managed_default_content_settings.popups";
 
 // Dictionary for storing the set of known background pages (keys are extension
 // IDs of background page owners, value is a boolean that is true if the user
 // needs to acknowledge this page.
 const char kKnownBackgroundPages[] = "background_pages.known";
 }  // namespace prefs