Index: Defines.php
===================================================================
RCS file: /cvsroot/wikipedia/phase3/includes/Defines.php,v
retrieving revision 1.33
diff -u -r1.33 Defines.php
--- Defines.php	27 Sep 2005 19:48:54 -0000	1.33
+++ Defines.php	9 Oct 2005 17:27:42 -0000
@@ -138,4 +138,12 @@
 define( 'MW_DATE_ISO', 'ISO 8601' );
 /**#@-*/
 
+/**#@+
+ * Language detection selectors;
+ * see $wgDetectLanguage and User::detectLanguage() 
+ */
+define( 'LANG_USE_CONTENT', '0' );    #no detection
+define( 'LANG_PREFER_CONTENT', '1' ); #use content language if accepted
+define( 'LANG_PREFER_CLIENT', '2' );  #use language most preferred by the client
+/**#@-*/
 ?>
Index: DefaultSettings.php
===================================================================
RCS file: /cvsroot/wikipedia/phase3/includes/DefaultSettings.php,v
retrieving revision 1.377
diff -u -r1.377 DefaultSettings.php
--- DefaultSettings.php	24 Sep 2005 00:49:55 -0000	1.377
+++ DefaultSettings.php	9 Oct 2005 17:27:45 -0000
@@ -511,6 +511,16 @@
 /** Site language code, should be one of ./languages/Language(.*).php */
 $wgLanguageCode     = 'en';
 
+/** 
+* Configures language detection for anonymous users.
+* Detection is based on the Accept-Language HTTP header.
+*
+* LANG_USE_CONTENT: always use the content language if not logged in
+* LANG_PREFER_CONTENT: if the content language is in the Accept-Language header, use it.
+* LANG_PREFER_CLIENT: use the language most prefered by the client (first in the list in Accept-Language).
+*/
+$wgDetectLanguage   = LANG_USE_CONTENT;
+
 /** Treat language links as magic connectors, not inline links */
 $wgInterwikiMagic	= true;
 
Index: OutputPage.php
===================================================================
RCS file: /cvsroot/wikipedia/phase3/includes/OutputPage.php,v
retrieving revision 1.244
diff -u -r1.244 OutputPage.php
--- OutputPage.php	6 Oct 2005 14:20:45 -0000	1.244
+++ OutputPage.php	9 Oct 2005 17:27:47 -0000
@@ -349,14 +349,17 @@
 	}
 
 	function sendCacheControl() {
-		global $wgUseSquid, $wgUseESI;
+		global $wgUseSquid, $wgUseESI, $wgDetectLanguage;
 
 		if ($this->mETag)
 			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
-		header( 'Vary: Accept-Encoding, Cookie' );
+		# if language detection is enabled, use different caches for different languages
+		if ($wgDetectLanguage) header( 'Vary: Accept-Encoding, Cookie, Accept-Language' );
+		else header( 'Vary: Accept-Encoding, Cookie' );
+		
 		if( !$this->uncacheableBecauseRequestvars() && $this->mEnableClientCache ) {
 			if( $wgUseSquid && ! isset( $_COOKIE[ini_get( 'session.name') ] ) &&
 			  ! $this->isPrintable() && $this->mSquidMaxage != 0 )
Index: User.php
===================================================================
RCS file: /cvsroot/wikipedia/phase3/includes/User.php,v
retrieving revision 1.185
diff -u -r1.185 User.php
--- User.php	8 Oct 2005 20:15:36 -0000	1.185
+++ User.php	9 Oct 2005 17:27:50 -0000
@@ -328,14 +328,109 @@
 
 		/**
 		 * default language setting
+		 *
+		 * TODO: avoid calling detectLanguage for
+		 *       logged in users!
 		 */
-		$variant = $wgContLang->getPreferredVariant();
+		$variant = User::detectLanguage();
 		$defOpt['variant'] = $variant;
 		$defOpt['language'] = $variant;
 
 		return $defOpt;
 	}
-
+	
+	/**
+	 * Detect the default language, according to $wgDetectLanguage.
+	 * If $wgDetectLanguage is LANG_USE_CONTENT, this just returns
+	 * the content language code. Otherwise, it tries to match 
+	 * the HTTP_ACCEPT_LANGUAGE header sent by the browser to an
+	 * interface language.
+	 *
+	 * @return string the language code
+	 * @static
+	 * @access private
+	 */
+	function detectLanguage() {
+		global $wgDetectLanguage, $wgContLang;
+		
+		/**
+		* get content language
+		*/
+		$contLang = $wgContLang->getPreferredVariant();
+		
+		if (!$wgDetectLanguage) {
+			return $contLang;
+		}
+		
+		/**
+		* get accepted languages from Accept-Languages
+		* HTTP header.
+		*/
+		$l= $_SERVER["HTTP_ACCEPT_LANGUAGE"];
+		
+		if (empty($l)) return $contLang;
+		
+		$l= split(',',$l);
+		
+		/**
+		* normalize accepted languages
+		*/
+		$languages= array();
+		foreach ($l as $lan) {
+			$lan= trim($lan);
+			
+			$idx= strpos($lan,';');
+			if ($idx !== false) {
+				#HACK: qualifiers are ignored, order is relevant!
+				$lan= substr($lan,0,$idx);
+				$lan= trim($lan);
+			}
+
+			$languages[]= $lan;
+			
+			$idx= strpos($lan,'-');
+			if ($idx !== false) {
+				$lan= substr($lan,0,$idx);
+				$languages[]= $lan;
+			}
+		}
+
+		/**
+		* see if the content language is accepted by the 
+		* client.
+		*/
+		if ( ($wgDetectLanguage == LANG_PREFER_CONTENT) 
+			&& in_array($contLang,$languages) ) {
+			return $contLang;
+		}
+		
+		/**
+		* look for a language that is acceptable to the client
+		* and known to the wiki.
+		*/
+		$known = $wgContLang->getLanguageNames();
+		foreach($known as $code => $name) {
+			/**
+			* TODO: only accept languages for which an implementation exists.
+			*       this is disabled, because it's slow. Note that this code is
+			*       executed for every page request!
+			*/
+			/*
+			global $IP;
+			$langfile="$IP/languages/Language".str_replace('-', '_', ucfirst($code)).".php";
+			if(!file_exists($langfile)) {
+				continue;
+			}
+			*/
+			
+			if (in_array($code,$languages)) {
+				return $code;
+			}
+		}
+			
+		return $contLang;
+	}
+	
 	/**
 	 * Get a given default option value.
 	 *