[6.0] Fix incorrect language tag comparison (#45947)

* Fix incorrect language tag comparison

* Fix Tainted detection

Author: Fedik

plugins/system/languagefilter/src/Extension/LanguageFilter.php

@@ -373,13 +373,13 @@ public function parseRule(&$router, &$uri)
             } elseif ($this->params->get('remove_default_prefix', 0)) {
                 // We don't have a prefix for the default language
                 $uri->setVar('lang', $this->default_lang);
-            } else {
+            } elseif (!isset($this->sefs[$lang])) {
                 // No language is set, so we want to redirect to the right language
                 $router->setTainted();
             }
 
             // The language was set both per SEF path and per query parameter. Query parameter takes precedence
-            if ($lang) {
+            if ($lang && isset($this->sefs[$sef])) {
                 $uri->setVar('lang', $lang);
                 $router->setTainted();
             }
@@ -422,8 +422,18 @@ public function setLanguageApplicationState(&$router, &$uri)
 
         // Our parse rule discovered a language
         if ($uri->hasVar('lang')) {
-            $lang_code = $uri->getVar('lang');
-        } else {
+            $uri_lang_code = $uri->getVar('lang');
+
+            // Check whether the tag exists, first check for full language tag, then for short tag
+            if (isset($this->lang_codes[$uri_lang_code])) {
+                $lang_code = $uri_lang_code;
+            } elseif (isset($this->sefs[$uri_lang_code])) {
+                // Check for short language tag
+                $lang_code = $this->sefs[$uri_lang_code]->lang_code;
+            }
+        }
+
+        if (!$lang_code) {
             /**
              * We don't know the language yet and want to discover it.
              * If we remove the default prefix, call by POST or have nolangfilter set,

plugins/system/sef/src/Extension/Sef.php

@@ -119,7 +119,7 @@ public function onAfterRoute(AfterRouteEvent $event)
         if ($router->isTainted()) {
             $parsedVars = $router->getVars();
 
-            if ($app->getLanguageFilter()) {
+            if ($app->getLanguageFilter() && isset($parsedVars['language'])) {
                 $parsedVars['lang'] = $parsedVars['language'];
                 unset($parsedVars['language']);
             }