diff --git a/phpBB/adm/index.php b/phpBB/adm/index.php
index 7a3997cdd7..6c142fde3f 100644
--- a/phpBB/adm/index.php
+++ b/phpBB/adm/index.php
@@ -147,7 +147,7 @@ function adm_page_header($page_title)
 		'ICON_SYNC'					=> '<img src="' . $phpbb_admin_path . 'images/icon_sync.gif" alt="' . $user->lang['RESYNC'] . '" title="' . $user->lang['RESYNC'] . '" />',
 		'ICON_SYNC_DISABLED'		=> '<img src="' . $phpbb_admin_path . 'images/icon_sync_disabled.gif" alt="' . $user->lang['RESYNC'] . '" title="' . $user->lang['RESYNC'] . '" />',
 
-		'S_USER_LANG'			=> $user->data['user_lang'],
+		'S_USER_LANG'			=> $user->lang['USER_LANG'],
 		'S_CONTENT_DIRECTION'	=> $user->lang['DIRECTION'],
 		'S_CONTENT_ENCODING'	=> 'UTF-8',
 		'S_CONTENT_DIR_LEFT'	=> $user->lang['LEFT'],
diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index 96c999e3ea..3c6a80fc37 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -3212,7 +3212,7 @@ function page_header($page_title = '', $display_online_list = true)
 		'S_REGISTERED_USER'		=> $user->data['is_registered'],
 		'S_IS_BOT'				=> $user->data['is_bot'],
 		'S_USER_PM_POPUP'		=> $user->optionget('popuppm'),
-		'S_USER_LANG'			=> $user->data['user_lang'],
+		'S_USER_LANG'			=> $user->lang['USER_LANG'],
 		'S_USER_BROWSER'		=> (isset($user->data['session_browser'])) ? $user->data['session_browser'] : $user->lang['UNKNOWN_BROWSER'],
 		'S_USERNAME'			=> $user->data['username'],
 		'S_CONTENT_DIRECTION'	=> $user->lang['DIRECTION'],
diff --git a/phpBB/install/index.php b/phpBB/install/index.php
index 96828fb939..172d296399 100755
--- a/phpBB/install/index.php
+++ b/phpBB/install/index.php
@@ -120,8 +120,8 @@ if (!empty($_SERVER['HTTP_ACCEPT_LANGUAGE']) && !$language)
 	$accept_lang_ary = explode(',', strtolower($_SERVER['HTTP_ACCEPT_LANGUAGE']));
 	foreach ($accept_lang_ary as $accept_lang)
 	{
-		// Set correct format ... guess full xx-yy form
-		$accept_lang = substr($accept_lang, 0, 2) . '-' . substr($accept_lang, 3, 2);
+		// Set correct format ... guess full xx_yy form
+		$accept_lang = substr($accept_lang, 0, 2) . '_' . substr($accept_lang, 3, 2);
 
 		if (file_exists($phpbb_root_path . 'language/' . $accept_lang))
 		{
@@ -130,7 +130,7 @@ if (!empty($_SERVER['HTTP_ACCEPT_LANGUAGE']) && !$language)
 		}
 		else
 		{
-			// No match on xx-yy so try xx
+			// No match on xx_yy so try xx
 			$accept_lang = substr($accept_lang, 0, 2);
 			if (file_exists($phpbb_root_path . 'language/' . $accept_lang))
 			{
@@ -311,7 +311,7 @@ class module
 		}
 
 		define('HEADER_INC', true);
-		global $template, $lang, $language, $stage, $phpbb_root_path;
+		global $template, $lang, $stage, $phpbb_root_path;
 
 		$template->assign_vars(array(
 			'L_CHANGE'				=> $lang['CHANGE'],
@@ -324,7 +324,7 @@ class module
 			'S_CONTENT_ENCODING' 	=> 'UTF-8',
 			'S_CONTENT_DIR_LEFT' 	=> $lang['LEFT'],
 			'S_CONTENT_DIR_RIGHT' 	=> $lang['RIGHT'],
-			'S_USER_LANG'			=> $language,
+			'S_USER_LANG'			=> $lang['USER_LANG'],
 			)
 		);
 
diff --git a/phpBB/language/en/common.php b/phpBB/language/en/common.php
index 1bccde25ce..1ec3fb6091 100644
--- a/phpBB/language/en/common.php
+++ b/phpBB/language/en/common.php
@@ -36,7 +36,7 @@ $lang = array_merge($lang, array(
 	'LEFT'				=> 'left',
 	'RIGHT'				=> 'right',
 	'DATE_FORMAT'		=> '|d M Y|',
-	'HTML_LANG'			=> 'en_EN',
+	'USER_LANG'			=> 'en-gb',
 
 	'1_DAY'			=> '1 day',
 	'1_MONTH'		=> '1 month',