fix: $this->request->setLocale() does not work for lang() in 404 controller

Fixes #5261

Author: kenjis

system/Exceptions/PageNotFoundException.php

@@ -11,6 +11,7 @@
 
 namespace CodeIgniter\Exceptions;
 
+use Config\Services;
 use OutOfBoundsException;
 
 class PageNotFoundException extends OutOfBoundsException implements ExceptionInterface
@@ -26,21 +27,37 @@ class PageNotFoundException extends OutOfBoundsException implements ExceptionInt
 
     public static function forPageNotFound(?string $message = null)
     {
-        return new static($message ?? lang('HTTP.pageNotFound'));
+        return new static($message ?? self::lang('HTTP.pageNotFound'));
     }
 
     public static function forEmptyController()
     {
-        return new static(lang('HTTP.emptyController'));
+        return new static(self::lang('HTTP.emptyController'));
     }
 
     public static function forControllerNotFound(string $controller, string $method)
     {
-        return new static(lang('HTTP.controllerNotFound', [$controller, $method]));
+        return new static(self::lang('HTTP.controllerNotFound', [$controller, $method]));
     }
 
     public static function forMethodNotFound(string $method)
     {
-        return new static(lang('HTTP.methodNotFound', [$method]));
+        return new static(self::lang('HTTP.methodNotFound', [$method]));
+    }
+
+    /**
+     * Get translated system message
+     *
+     * Use a non-shared Language instance in the Services.
+     * If a shared instance is created, the Language will
+     * have the current locale, so even if users call
+     * `$this->request->setLocale()` in the controller afterwards,
+     * the Language locale will not be changed.
+     */
+    private static function lang(string $line, array $args = []): string
+    {
+        $lang = Services::language(null, false);
+
+        return $lang->getLine($line, $args);
     }
 }