use lang query to change to default lang

Signed-off-by: Andy Miller <rhuk@mac.com>

Author: rhukster

system/src/Grav/Common/Language/Language.php

@@ -249,6 +249,26 @@ public function setActiveFromUri($uri)
 
         // if languages set
         if ($this->enabled()) {
+            // Check for explicit language override via ?lang= query parameter.
+            // This allows switching to any language (including the default language
+            // when include_default_lang is false and the URL has no language prefix).
+            $requestedLang = $_GET['lang'] ?? null;
+            if ($requestedLang) {
+                $requestedLang = strtolower($requestedLang);
+                if (in_array($requestedLang, $this->languages, true)) {
+                    $this->setActive($requestedLang);
+
+                    // Store in session.
+                    if (isset($this->grav['session']) && $this->grav['session']->isStarted()
+                        && $this->config->get('system.languages.session_store_active', true)
+                    ) {
+                        $this->grav['session']->active_language = $this->active;
+                    }
+
+                    return $uri;
+                }
+            }
+
             // Try setting language from prefix of URL (/en/blah/blah).
             if (preg_match($regex, $uri, $matches)) {
                 $this->lang_in_url = true;
@@ -263,36 +283,22 @@ public function setActiveFromUri($uri)
                     $this->grav['session']->active_language = $this->active;
                 }
             } else {
-                if ($this->config->get('system.languages.include_default_lang') === false) {
-                    // When include_default_lang is false, the default language has no URL prefix.
-                    // A URL without a language prefix IS the default language explicitly.
-                    $this->setActive($this->getDefault());
-
-                    // Store in session if language is different.
-                    if (isset($this->grav['session']) && $this->grav['session']->isStarted()
-                        && $this->config->get('system.languages.session_store_active', true)
-                        && $this->grav['session']->active_language != $this->active
-                    ) {
-                        $this->grav['session']->active_language = $this->active;
-                    }
-                } else {
-                    // Try getting language from the session, else no active.
-                    if (isset($this->grav['session']) && $this->grav['session']->isStarted() &&
-                        $this->config->get('system.languages.session_store_active', true)) {
-                        $this->setActive($this->grav['session']->active_language ?: null);
-                    }
-                    // if still null, try from http_accept_language header
-                    if ($this->active === null &&
-                        $this->config->get('system.languages.http_accept_language') &&
-                        $accept = $_SERVER['HTTP_ACCEPT_LANGUAGE'] ?? false) {
-                        $negotiator = new LanguageNegotiator();
-                        $best_language = $negotiator->getBest($accept, $this->languages);
-
-                        if ($best_language instanceof AcceptLanguage) {
-                            $this->setActive($best_language->getType());
-                        } else {
-                            $this->setActive($this->getDefault());
-                        }
+                // Try getting language from the session, else no active.
+                if (isset($this->grav['session']) && $this->grav['session']->isStarted() &&
+                    $this->config->get('system.languages.session_store_active', true)) {
+                    $this->setActive($this->grav['session']->active_language ?: null);
+                }
+                // if still null, try from http_accept_language header
+                if ($this->active === null &&
+                    $this->config->get('system.languages.http_accept_language') &&
+                    $accept = $_SERVER['HTTP_ACCEPT_LANGUAGE'] ?? false) {
+                    $negotiator = new LanguageNegotiator();
+                    $best_language = $negotiator->getBest($accept, $this->languages);
+
+                    if ($best_language instanceof AcceptLanguage) {
+                        $this->setActive($best_language->getType());
+                    } else {
+                        $this->setActive($this->getDefault());
                     }
                 }
             }