diff --git a/phpBB/install/index.php b/phpBB/install/index.php
index c0d5675e4d..96828fb939 100755
--- a/phpBB/install/index.php
+++ b/phpBB/install/index.php
@@ -110,17 +110,18 @@ include($phpbb_root_path . 'includes/template.' . $phpEx);
 include($phpbb_root_path . 'includes/acm/acm_file.' . $phpEx);
 include($phpbb_root_path . 'includes/cache.' . $phpEx);
 include($phpbb_root_path . 'includes/functions_admin.' . $phpEx);
+include($phpbb_root_path . 'includes/utf/utf_tools.' . $phpEx);
 
 // Try and load an appropriate language if required
 $language = request_var('language', '');
 
 if (!empty($_SERVER['HTTP_ACCEPT_LANGUAGE']) && !$language)
 {
-	$accept_lang_ary = explode(',', $_SERVER['HTTP_ACCEPT_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) . '_' . strtoupper(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/' . $accept_lang))
 		{
@@ -129,7 +130,7 @@ if (!empty($_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))
 			{
@@ -319,11 +320,11 @@ class module
 			'PAGE_TITLE'			=> $this->get_page_title(),
 			'T_IMAGE_PATH'			=> $phpbb_root_path . 'adm/images/',
 
-			'S_USER_LANG'			=> $language,
 			'S_CONTENT_DIRECTION' 	=> $lang['DIRECTION'],
 			'S_CONTENT_ENCODING' 	=> 'UTF-8',
 			'S_CONTENT_DIR_LEFT' 	=> $lang['LEFT'],
 			'S_CONTENT_DIR_RIGHT' 	=> $lang['RIGHT'],
+			'S_USER_LANG'			=> $language,
 			)
 		);
 
diff --git a/phpBB/install/install_install.php b/phpBB/install/install_install.php
index e8ebd7f726..9665957274 100755
--- a/phpBB/install/install_install.php
+++ b/phpBB/install/install_install.php
@@ -553,7 +553,7 @@ class install_install extends module
 		{
 			// Someone's been silly and tried calling this page direct
 			// So we send them back to the start to do it again properly
-			$this->p_master->redirect("index?mode=install");
+			$this->p_master->redirect("index.$phpEx?mode=install");
 		}
 
 		$s_hidden_fields = ($img_imagick) ? '<input type="hidden" name="img_imagick" value="' . addslashes($img_imagick) . '" />' : '';
@@ -725,7 +725,7 @@ class install_install extends module
 		{
 			// Someone's been silly and tried calling this page direct
 			// So we send them back to the start to do it again properly
-			$this->p_master->redirect("index?mode=install");
+			$this->p_master->redirect("index.$phpEx?mode=install");
 		}
 
 		$s_hidden_fields = ($img_imagick) ? '<input type="hidden" name="img_imagick" value="' . addslashes($img_imagick) . '" />' : '';
@@ -880,7 +880,7 @@ class install_install extends module
 		{
 			// Someone's been silly and tried calling this page direct
 			// So we send them back to the start to do it again properly
-			$this->p_master->redirect("index?mode=install");
+			$this->p_master->redirect("index.$phpEx?mode=install");
 		}
 
 		$s_hidden_fields = ($img_imagick) ? '<input type="hidden" name="img_imagick" value="' . addslashes($img_imagick) . '" />' : '';
@@ -964,7 +964,7 @@ class install_install extends module
 		{
 			// Someone's been silly and tried calling this page direct
 			// So we send them back to the start to do it again properly
-			$this->p_master->redirect("index?mode=install");
+			$this->p_master->redirect("index.$phpEx?mode=install");
 		}
 
 		$cookie_domain = ($server_name != '') ? $server_name : (!empty($_SERVER['SERVER_NAME'])) ? $_SERVER['SERVER_NAME'] : getenv('SERVER_NAME');