Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.264
diff -u -p -r1.264 bootstrap.inc
--- includes/bootstrap.inc	14 Jan 2009 12:15:38 -0000	1.264
+++ includes/bootstrap.inc	15 Jan 2009 18:36:13 -0000
@@ -130,15 +130,15 @@ define('DRUPAL_BOOTSTRAP_SESSION', 4);
 define('DRUPAL_BOOTSTRAP_VARIABLES', 5);
 
 /**
- * Seventh bootstrap phase: load bootstrap.inc and module.inc, start
- * the variable system and try to serve a page from the cache.
+ * Seventh bootstrap phase: find out the language of the page.
  */
-define('DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE', 6);
+define('DRUPAL_BOOTSTRAP_LANGUAGE', 6);
 
 /**
- * Eighth bootstrap phase: find out language of the page.
+ * Eighth bootstrap phase: load bootstrap.inc and module.inc, start
+ * the variable system and try to serve a page from the cache.
  */
-define('DRUPAL_BOOTSTRAP_LANGUAGE', 7);
+define('DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE', 7);
 
 /**
  * Nineth bootstrap phase: set $_GET['q'] to Drupal path of request.
@@ -1062,14 +1062,14 @@ function drupal_anonymous_user($session 
  *     DRUPAL_BOOTSTRAP_ACCESS: identify and reject banned hosts.
  *     DRUPAL_BOOTSTRAP_SESSION: initialize session handling.
  *     DRUPAL_BOOTSTRAP_VARIABLES: initialize variable handling.
+ *     DRUPAL_BOOTSRAP_LANGUAGE: identify the language used on the page.
  *     DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE: load bootstrap.inc and module.inc, start
  *       the variable system and try to serve a page from the cache.
- *     DRUPAL_BOOTSTRAP_LANGUAGE: identify the language used on the page.
  *     DRUPAL_BOOTSTRAP_PATH: set $_GET['q'] to Drupal path of request.
  *     DRUPAL_BOOTSTRAP_FULL: Drupal is fully loaded, validate and fix input data.
  */
 function drupal_bootstrap($phase = NULL) {
-  static $phases = array(DRUPAL_BOOTSTRAP_CONFIGURATION, DRUPAL_BOOTSTRAP_EARLY_PAGE_CACHE, DRUPAL_BOOTSTRAP_DATABASE, DRUPAL_BOOTSTRAP_ACCESS, DRUPAL_BOOTSTRAP_SESSION, DRUPAL_BOOTSTRAP_VARIABLES, DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE, DRUPAL_BOOTSTRAP_LANGUAGE, DRUPAL_BOOTSTRAP_PATH, DRUPAL_BOOTSTRAP_FULL), $completed_phase = -1;
+  static $phases = array(DRUPAL_BOOTSTRAP_CONFIGURATION, DRUPAL_BOOTSTRAP_EARLY_PAGE_CACHE, DRUPAL_BOOTSTRAP_DATABASE, DRUPAL_BOOTSTRAP_ACCESS, DRUPAL_BOOTSTRAP_SESSION, DRUPAL_BOOTSTRAP_VARIABLES, DRUPAL_BOOTSTRAP_LANGUAGE, DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE, DRUPAL_BOOTSTRAP_PATH, DRUPAL_BOOTSTRAP_FULL), $completed_phase = -1;
 
   if (isset($phase)) {
     while ($phases && $phase > $completed_phase) {
@@ -1093,7 +1093,7 @@ function drupal_get_bootstrap_phase() {
 }
 
 function _drupal_bootstrap($phase) {
-  global $conf;
+  global $conf, $language, $language_redirect;
 
   switch ($phase) {
 
@@ -1147,16 +1147,34 @@ function _drupal_bootstrap($phase) {
       $conf = variable_init(isset($conf) ? $conf : array());
       break;
 
+    case DRUPAL_BOOTSTRAP_LANGUAGE:
+      drupal_init_language();
+      break;
+
     case DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE:
       $cache_mode = variable_get('cache', CACHE_DISABLED);
       // Get the page from the cache.
-      $cache = $cache_mode == CACHE_DISABLED ? '' : page_get_cache();
       // If the skipping of the bootstrap hooks is not enforced, call hook_boot.
-      if (!$cache || $cache_mode != CACHE_AGGRESSIVE) {
+      if ($cache_mode != CACHE_AGGRESSIVE) {
         // Load module handling.
         require_once DRUPAL_ROOT . '/includes/module.inc';
         module_invoke_all('boot');
       }
+      // If the language has been reset from the default, redirect
+      // to the new language.
+      if ($language_redirect && (($default_language = language_default()) != $language)) {
+        // Load modules required for hook_exit.
+        module_invoke_all('exit');
+        // We need the path system.
+        drupal_bootstrap(DRUPAL_BOOTSTRAP_PATH);
+        require_once DRUPAL_ROOT . '/includes/common.inc';
+        $path = drupal_get_normal_path($_GET['q'], $default_language->language);
+        drupal_goto($path);
+      }
+
+      // Fetch the page from cache.
+      $cache = $cache_mode == CACHE_DISABLED ? '' : page_get_cache();
+
       // If there is a cached page, display it.
       if ($cache) {
         drupal_page_cache_header($cache);
@@ -1167,14 +1185,16 @@ function _drupal_bootstrap($phase) {
         // We are done.
         exit;
       }
+      // If not skipped above, call hook_boot now.
+      if ($cache_mode == CACHE_AGGRESSIVE) {
+        require_once DRUPAL_ROOT . '/includes/module.inc';
+        module_invoke_all('boot');
+      }
+
       // Prepare for non-cached page workflow.
       drupal_page_header();
       break;
 
-    case DRUPAL_BOOTSTRAP_LANGUAGE:
-      drupal_init_language();
-      break;
-
     case DRUPAL_BOOTSTRAP_PATH:
       require_once DRUPAL_ROOT . '/includes/path.inc';
       // Initialize $_GET['q'] prior to loading modules and invoking hook_init().
Index: includes/language.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/language.inc,v
retrieving revision 1.18
diff -u -p -r1.18 language.inc
--- includes/language.inc	2 Jan 2009 23:37:32 -0000	1.18
+++ includes/language.inc	15 Jan 2009 18:36:13 -0000
@@ -7,10 +7,14 @@
  */
 
 /**
- *  Choose a language for the page, based on language negotiation settings.
+ * Choose a language for the page, based on language negotiation settings.
+ *
+ * @return
+ *   Boolean indicating whether the language set is valid for the current
+ *   path.
  */
 function language_initialize() {
-  global $user;
+  global $user, $language_redirect;
 
   // Configured presentation language mode.
   $mode = variable_get('language_negotiation', LANGUAGE_NEGOTIATION_NONE);
@@ -52,13 +56,19 @@ function language_initialize() {
       break;
   }
 
+  // We should reach this point only if LANGUAGE_NEGOTIATION_PATH is set
+  // but no valid prefix was found or if some custom value has been set for
+  // language_negotiation.
+
   // User language.
   if ($user->uid && isset($languages[$user->language])) {
+    $language_redirect = TRUE;
     return $languages[$user->language];
   }
 
   // Browser accept-language parsing.
   if ($language = language_from_browser()) {
+    $language_redirect = TRUE;
     return $language;
   }
 
Index: modules/simpletest/tests/bootstrap.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/tests/bootstrap.test,v
retrieving revision 1.10
diff -u -p -r1.10 bootstrap.test
--- modules/simpletest/tests/bootstrap.test	14 Jan 2009 12:15:38 -0000	1.10
+++ modules/simpletest/tests/bootstrap.test	15 Jan 2009 18:36:14 -0000
@@ -88,6 +88,76 @@ class BootstrapIPAddressTestCase extends
   }
 }
 
+/**
+ * Test page caching with language negotiation.
+ */
+class BootstrapPageCacheWithLanguageFallbackTestCase extends DrupalWebTestCase {
+
+  function getInfo() {
+    return array(
+      'name' => t('Page cache test with language negotiation'),
+      'description' => t('Enable the page cache and language negotiation, ensure that cached pages are served in the correct language.'),
+      'group' => t('Bootstrap')
+    );
+  }
+
+  function setUp() {
+    parent::setUp('locale');
+    $web_user = $this->drupalCreateUser(array('administer languages', 'access administration pages'));
+    $this->drupalLogin($web_user);
+
+    // Enable French language.
+    $edit = array();
+    $edit['langcode'] = 'fr';
+
+    $this->drupalPost('admin/settings/language/add', $edit, t('Add language'));
+    $this->drupalLogout($web_user);
+
+    // Set language negotiation to "Path prefix with fallback".
+    variable_set('language_negotiation', LANGUAGE_NEGOTIATION_PATH);
+
+    // Force inclusion of language.inc.
+    drupal_init_language();
+    // Enable the page cache.
+    variable_set('cache', CACHE_NORMAL);
+  }
+
+  /**
+   * Test page caching with language fallback.
+   */
+  function testPageCacheLanguageFallback() {
+
+    // Visit the root path with browser language preference set to French.
+    // Since this is in the default site language (English), the page should
+    // not be cached for this request.
+    $this->drupalGet('', array(), array('Accept-Language: fr'));
+    $this->assertFalse(cache_get(url('', array('absolute' => TRUE)), 'cache_page'), t('Page has not been cached.'));
+    $this->assertFalse($this->drupalGetHeader('Etag'), t('Page not served from cache.'));
+
+    // The visitor should be redirected to a version of the page with their
+    // language prefix.
+    $this->assertRaw('xml:lang="fr"', t('Page returned in the correct language.'));
+
+    // When requesting the page a second time, the browser should be
+    // redirected to a cached version of the page.
+    $this->drupalGet('', array(), array('Accept-Language: fr'));
+    $this->assertRaw('xml:lang="fr"', t('Page returned in the correct language.'));
+    $this->assertTrue($this->drupalGetHeader('Etag'), t('Page served from cache.'));
+
+    // Visit the page again with browser language set to English, and confirm that
+    // it's returned in the correct language.
+    $this->drupalGet('', array(), array('Accept-Language: en'));
+    $this->assertFalse($this->drupalGetHeader('Etag'), t('Page not served from cache.'));
+    $this->assertTrue(cache_get(url('', array('absolute' => TRUE)), 'cache_page'), t('Page has been cached.'));
+    $this->assertRaw('xml:lang="en"', t('Page returned in the correct language.'));
+
+    // Ensure that the page is cached correctly when requested again.
+    $this->drupalGet('', array(), array('Accept-Language: en'));
+    $this->assertTrue($this->drupalGetHeader('Etag'), t('Page served from cache'));
+    $this->assertRaw('xml:lang="en"', t('Page returned in the correct language.'));
+  }
+}
+
 class BootstrapPageCacheTestCase extends DrupalWebTestCase {
 
   function getInfo() {