Index: modules/simpletest/drupal_web_test_case.php
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/drupal_web_test_case.php,v
retrieving revision 1.207
diff -u -r1.207 drupal_web_test_case.php
--- modules/simpletest/drupal_web_test_case.php	31 Mar 2010 20:05:06 -0000	1.207
+++ modules/simpletest/drupal_web_test_case.php	3 Apr 2010 11:09:38 -0000
@@ -1149,6 +1149,9 @@
     drupal_static_reset();
 
     include_once DRUPAL_ROOT . '/includes/install.inc';
+
+    // Avoid exceptions from t() during install if the current language is not 'en'.
+    $GLOBALS['language']->language = 'en';
     drupal_install_system();
 
     $this->preloadRegistry();