Index: includes/OutputPage.php
===================================================================
--- includes/OutputPage.php	(revision 59487)
+++ includes/OutputPage.php	(working copy)
@@ -50,6 +50,7 @@
 
 	private $mIndexPolicy = 'index';
 	private $mFollowPolicy = 'follow';
+	private $mVaryHeader = array();
 
 	/**
 	 * Constructor
@@ -807,20 +808,45 @@
 
 	/** Get a complete X-Vary-Options header */
 	public function getXVO() {
+		$this->addVaryHeader( 'Accept-Encoding', 'list-contains', 'gzip' );
+		$this->addVaryHeader( 'Cookie' );
 		$cvCookies = $this->getCacheVaryCookies();
-		$xvo = 'X-Vary-Options: Accept-Encoding;list-contains=gzip,Cookie;';
+		foreach ( $cvCookies as $cookieName ) {
+			$this->addVaryHeader( 'Cookie', 'string-contains', $cookieName );
+		}
+		$xvo = 'X-Vary-Options: ';
 		$first = true;
-		foreach ( $cvCookies as $cookieName ) {
+		foreach ( $this->mVaryHeader as $header => $options ) {
 			if ( $first ) {
 				$first = false;
 			} else {
-				$xvo .= ';';
+				$xvo .= ', ';
 			}
-			$xvo .= 'string-contains=' . $cookieName;
+			$xvo .= $header;
+			foreach ( $options as $option => $values ) {
+				foreach ( $values as $value ) {
+					$xvo .= '; ' . $option . '=' . $value;
+				}
+			}
 		}
 		return $xvo;
 	}
 
+	public function addVaryHeader( $header, $option = false, $value = false ) {
+		$header = strtolower( $header );
+		if ( !array_key_exists( $header, $this->mVaryHeader ) ) {
+			$this->mVaryHeader[$header] = array();
+		}
+		if ( $option ) {
+			if ( !array_key_exists( $option, $this->mVaryHeader[$header] ) ) {
+				$this->mVaryHeader[$header][$option] = array();
+			}
+			if ( !in_array( $value, $this->mVaryHeader[$header][$option] ) ) {
+				$this->mVaryHeader[$header][$option][] = $value;
+			}
+		}
+	}
+
 	public function sendCacheControl() {
 		global $wgUseSquid, $wgUseESI, $wgUseETag, $wgSquidMaxage, $wgRequest, $wgUseXVO;
 
@@ -828,15 +854,16 @@
 		if ($wgUseETag && $this->mETag)
 			$response->header("ETag: $this->mETag");
 
-		# don't serve compressed data to clients who can't handle it
-		# maintain different caches for logged-in users and non-logged in ones
-		$response->header( 'Vary: Accept-Encoding, Cookie' );
-
 		if ( $wgUseXVO ) {
 			# Add an X-Vary-Options header for Squid with Wikimedia patches
 			$response->header( $this->getXVO() );
 		}
 
+		# don't serve compressed data to clients who can't handle it
+		# maintain different caches for logged-in users and non-logged in ones
+		# $this->mVaryHeader is not filled until getXVO is called
+		$response->header( 'Vary: ' . join( ', ', array_keys( $this->mVaryHeader ) ) );
+
 		if( !$this->uncacheableBecauseRequestVars() && $this->mEnableClientCache ) {
 			if( $wgUseSquid && session_id() == '' &&
 			  ! $this->isPrintable() && $this->mSquidMaxage != 0 && !$this->haveCacheVaryCookies() )
Index: languages/LanguageConverter.php
===================================================================
--- languages/LanguageConverter.php	(revision 59487)
+++ languages/LanguageConverter.php	(working copy)
@@ -130,7 +130,7 @@
 	 * @public
 	 */
 	function getPreferredVariant( $fromUser = true ) {
-		global $wgUser, $wgRequest, $wgVariantArticlePath, $wgDefaultLanguageVariant;
+		global $wgUser, $wgRequest, $wgVariantArticlePath, $wgDefaultLanguageVariant, $wgOut;
 
 		if($this->mPreferredVariant)
 			return $this->mPreferredVariant;
@@ -185,6 +185,11 @@
 			// variable in case this is called before the user's
 			// preference is loaded
 			if( array_key_exists( 'HTTP_ACCEPT_LANGUAGE', $_SERVER ) ) {
+
+				foreach ( $this->mVariants as $variant ) {
+					$wgOut->addVaryHeader( 'Accept-Language', 'string-contains', $variant );
+				}
+
 				$acceptLanguage = strtolower( $_SERVER['HTTP_ACCEPT_LANGUAGE'] );
 				
 				// explode by comma