Translate pages, areas, menus, forms and posts field by field instead of rebuilding them

A site can have further languages (Settings → Languages). A page is built once; each language
adds only its texts, keyed by the stable block IDs, plus its own address under /en/… (ADR 111,
document schema v27, migration 20261009000100 for page_translation).

- Editor: DE | EN switch, a list of all texts with original, state (missing, translated,
  original changed) and filter; structure stays with the main language. Undo, drafts,
  publishing and revisions cover all languages at once.
- Website: /en and translated slugs, lang, canonical, hreflang with x-default, og:locale,
  sitemap; links to translated pages follow the language; a language switch block.
- Header, footer and linked sections translate the same way; menu entries carry labels per
  language; fixed template texts come from a small dictionary.
- Forms: labels, help, options, button and success message per language; messages and the
  step script speak the language, the submission and the email stay in the main language.
- Posts, archives, category names, consent text and the 404 page follow the language.
- Single-language sites see none of it and never touch the new table.

The forms administration becomes an overview with one row per form and its own edit page;
fields are one line each with details collapsed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/Controller/FormController.php

@@ -3,6 +3,7 @@
 namespace App\Controller;
 
 use App\Content\FormRepository;
+use App\Content\Languages;
 use App\Content\MenuRepository;
 use App\Content\PageRepository;
 use App\Content\SiteSettings;
@@ -32,6 +33,7 @@ final class FormController extends AbstractController
         private Turnstile $turnstile,
         private string $secret,
         private string $siteOrigin,
+        private Languages $languages,
     ) {
     }
 
@@ -56,10 +58,19 @@ final class FormController extends AbstractController
             // noch einmal.
             || !$this->turnstile->passed($request->request->getString('cf-turnstile-response'), $request->getClientIp());
 
-        $checked = $this->forms->check($form, $request->request->all());
+        // Abgeschickt von einer übersetzten Seite (ADR 111): Meldungen in dieser Sprache, und der
+        // Weg zurück führt auf die übersetzte Seite - sofern es sie gibt.
+        $language = $request->request->getString('language');
+        $translatedPath = null;
+        if ($this->languages->isExtra($language)) {
+            $translatedPath = $this->pages->translatedPaths($page['id'])[$language] ?? null;
+        }
+        $language = null === $translatedPath ? null : $language;
+
+        $checked = $this->forms->check($form, $request->request->all(), $language);
         if (!$silentlyDropped && [] !== $checked['errors']) {
             // Re-render the page the form sits on, with the entered values and the messages.
-            return $this->renderPage($request, $page, $form, $checked);
+            return $this->renderPage($request, $page, $form, $checked, null === $language ? null : ($page['path'] === $this->settings->homePath() ? $language : $language.'/'.$translatedPath));
         }
         if (!$silentlyDropped) {
             $submission = $this->forms->store($form['id'], $checked['values'], $checked['consent'], $senderHash);
@@ -69,7 +80,9 @@ final class FormController extends AbstractController
         }
 
         // Post/Redirect/Get so a reload does not send the message twice.
-        return $this->redirect($this->settings->publicPath($path).'?gesendet='.rawurlencode($slug).'#'.rawurlencode($request->request->getString('block')), 303);
+        $back = null === $language ? $this->settings->publicPath($path) : '/'.$language.($page['path'] === $this->settings->homePath() ? '' : '/'.$translatedPath);
+
+        return $this->redirect($back.'?gesendet='.rawurlencode($slug).'#'.rawurlencode($request->request->getString('block')), 303);
     }
 
     /** The signed timestamp makes the age of the form checkable without storing anything. */
@@ -128,7 +141,7 @@ final class FormController extends AbstractController
      * vergass, sah eine Seite ohne Gestaltung. Jetzt geht der Weg durch dieselbe Stelle wie jeder
      * andere Aufruf, und die Formularzustaende werden als Anfrageattribut mitgereicht.
      */
-    private function renderPage(Request $request, array $page, array $form, array $checked): Response
+    private function renderPage(Request $request, array $page, array $form, array $checked, ?string $translatedAddress = null): Response
     {
         // Nur das abgeschickte Formular zeigt Meldungen und behaelt seine Eingaben - wo auch immer
         // es auf der Seite steht: im Inhalt, im Kopf, im Fuss oder in einer verknuepften Sektion.
@@ -137,7 +150,7 @@ final class FormController extends AbstractController
 
         // Die Startseite antwortet unter "/" - mit ihrem eigenen Pfad wuerde sie dorthin umleiten,
         // und aus der Fehlermeldung wuerde eine Weiterleitung ohne Meldung.
-        $adresse = $page['path'] === $this->settings->homePath() ? '' : (string) $page['path'];
+        $adresse = $translatedAddress ?? ($page['path'] === $this->settings->homePath() ? '' : (string) $page['path']);
         $antwort = $this->forward('App\Controller\PageController::page', [
             'path' => $adresse,
             'request' => $request->duplicate(null, null, ['kant_form_state' => $zustaende, '_route' => 'page']),