Index: includes/install.core.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/install.core.inc,v
retrieving revision 1.48
diff -u -p -r1.48 install.core.inc
--- includes/install.core.inc	28 Dec 2010 18:17:27 -0000	1.48
+++ includes/install.core.inc	29 Dec 2010 10:38:56 -0000
@@ -1370,8 +1370,19 @@ function install_profile_modules(&$insta
 function install_import_locales(&$install_state) {
   include_once DRUPAL_ROOT . '/includes/locale.inc';
   $install_locale = $install_state['parameters']['locale'];
-  // Enable installation language as default site language.
-  locale_add_language($install_locale, NULL, NULL, NULL, '', NULL, 1, TRUE);
+  
+  include_once DRUPAL_ROOT . '/includes/iso.inc';
+  $predefined = _locale_get_predefined_list();
+  if (!isset($predefined[$install_locale])) {
+    // Drupal does not know about this language, so we prefill its values with
+    // our best guess. The user will be able to edit afterwards.
+    locale_add_language($install_locale, $install_locale, $install_locale, LANGUAGE_LTR, '', '', TRUE, TRUE);
+  }
+  else {
+    // A known predefined language, details will be filled in properly.
+    locale_add_language($install_locale, NULL, NULL, NULL, '', '', TRUE, TRUE);
+  }
+  
   // Collect files to import for this language.
   $batch = locale_batch_by_language($install_locale, NULL);
   if (!empty($batch)) {