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/EditorController.php

@@ -7,15 +7,18 @@ use App\Content\DemoContent;
 use App\Content\DocumentValidator;
 use App\Content\FontLibrary;
 use App\Content\FormRepository;
+use App\Content\Languages;
 use App\Content\MenuRepository;
 use App\Content\PageRepository;
 use App\Content\PartialRepository;
 use App\Content\PostLayouts;
 use App\Content\PostRepository;
 use App\Content\RedirectRepository;
+use App\Content\SiteSettings;
 use App\Content\StyleCompiler;
 use App\Content\StyleSchema;
 use App\Content\Theme;
+use App\Content\Translations;
 use App\Domain\InvalidDocument;
 use App\Domain\InvalidPage;
 use App\Domain\StaleWrite;
@@ -31,7 +34,7 @@ use Symfony\Component\Security\Csrf\CsrfTokenManagerInterface;
 #[Route('/%kant.admin_path%')]
 final class EditorController extends AbstractController
 {
-    public function __construct(private PageRepository $pages, private DocumentValidator $validator, private MenuRepository $menus, private PostRepository $posts, private Theme $theme, private StyleCompiler $styles, private RedirectRepository $redirects, private PartialRepository $partials, private CustomCode $code, private FontLibrary $fonts, private CsrfTokenManagerInterface $csrf, private RequestStack $requests, private PluginRegistry $plugins, private FormRepository $forms, private PostRepository $postsForPreview)
+    public function __construct(private PageRepository $pages, private DocumentValidator $validator, private MenuRepository $menus, private PostRepository $posts, private Theme $theme, private StyleCompiler $styles, private RedirectRepository $redirects, private PartialRepository $partials, private CustomCode $code, private FontLibrary $fonts, private CsrfTokenManagerInterface $csrf, private RequestStack $requests, private PluginRegistry $plugins, private FormRepository $forms, private PostRepository $postsForPreview, private Languages $languages, private SiteSettings $siteSettings)
     {
     }
 
@@ -440,8 +443,9 @@ final class EditorController extends AbstractController
         if (!$this->isCsrfTokenValid('editor', $request->headers->get('X-CSRF-Token'))) {
             return $this->json(['error' => 'Deine Sitzung ist abgelaufen. Bitte melde dich erneut an.'], 403);
         }
-        if (strlen($request->getContent()) > 270000) {
-            return $this->json(['error' => 'Die Seite ist zu groß (maximal 256 KiB Inhalt).'], 413);
+        // Eine Seite darf 256 KiB haben, mit ihren Übersetzungen zusammen 1 MiB (ADR 111).
+        if (strlen($request->getContent()) > 1100000) {
+            return $this->json(['error' => 'Die Seite ist zu groß (maximal 256 KiB Inhalt, mit Übersetzungen 1 MiB).'], 413);
         }
         $page = $this->page($id);
         try {
@@ -456,20 +460,30 @@ final class EditorController extends AbstractController
                     throw new \InvalidArgumentException();
                 }
                 $this->validator->validate($document, writing: true);
+                // Die Vorschau einer Übersetzung ist dieselbe Seite mit den übersetzten Texten -
+                // genau so, wie die Website sie in dieser Sprache ausliefert.
+                $language = $body['language'] ?? null;
+                $locale = is_string($language) && $this->languages->isExtra($language) ? $language : $this->languages->main();
+                $seoTitle = $locale === $this->languages->main() ? ($page['seo_title'] ?? null) : ($document['translations'][$locale]['seoTitle'] ?? '');
+                $document = $locale === $this->languages->main() ? Translations::strip($document) : Translations::apply($document, $locale);
+                $request->attributes->set('kant_alternates', array_map(fn (string $code): array => [...$this->languages->describe($code), 'locale' => $code, 'href' => '#', 'current' => $code === $locale], $this->languages->all()));
+
+                $request->attributes->set('kant_locale', $locale);
+                $localise = fn (array $doc): array => $locale === $this->languages->main() ? Translations::strip($doc) : Translations::apply($doc, $locale);
 
                 $theme = $this->theme->load();
                 $areas = [];
                 foreach (['header', 'footer'] as $kind) {
                     $area = $this->partials->findByKind($kind);
                     if (null !== $area) {
-                        $areas[$kind] = $area['document'];
+                        $areas[$kind] = $localise($area['document']);
                     }
                 }
                 $sections = [];
                 foreach ($this->partials->referencedSlugs($document) as $slug) {
                     $section = $this->partials->resolveSection($slug);
                     if (null !== $section) {
-                        $sections[$slug] = $section['document'];
+                        $sections[$slug] = $localise($section['document']);
                     }
                 }
                 // Wie auf der Website: die zweite Verknüpfung derselben Sektion bekommt eigene Kennungen.
@@ -485,7 +499,7 @@ final class EditorController extends AbstractController
                 }
                 $navigation = [];
                 foreach ($this->menus->all() as $slot => $menu) {
-                    $navigation[$slot] = $this->menus->resolve($menu['items'], (string) $page['path']);
+                    $navigation[$slot] = $this->menus->resolve($menu['items'], (string) $page['path'], language: $locale === $this->languages->main() ? null : $locale);
                 }
 
                 // Die Vorschau zeigt dieselbe Ausgabe wie die Website - einschliesslich eigenem
@@ -496,14 +510,14 @@ final class EditorController extends AbstractController
                 foreach ($documents as $doc) {
                     $styles .= $this->styles->compileDocument($doc).$this->code->compileDocument($doc);
                 }
-                $forms = $this->previewForms($documents, $page);
+                $forms = $this->previewForms($documents, $page, $locale === $this->languages->main() ? null : $locale);
                 foreach ($forms as $state) {
                     if (null !== $state['form']) {
                         $styles .= $this->forms->css($state['form'], $theme);
                     }
                 }
 
-                return $this->render('page.html.twig', ['page' => [...$page, 'document' => $document], 'canonical' => '', 'editing' => true, 'navigation' => $navigation, 'areas' => $areas, 'sections' => $sections, 'needsTabs' => false, 'forms' => $forms, 'pluginStyles' => $this->plugins->assetsFor($documents)['styles'], 'pageStyles' => $styles, 'localFonts' => $this->fonts->hasLocal($theme) ? $this->fonts->preload($theme) : []]);
+                return $this->render('page.html.twig', ['page' => [...$page, 'document' => $document, 'locale' => $locale, 'seo_title' => $seoTitle], 'canonical' => '', 'editing' => true, 'navigation' => $navigation, 'areas' => $areas, 'sections' => $sections, 'needsTabs' => false, 'forms' => $forms, 'pluginStyles' => $this->plugins->assetsFor($documents)['styles'], 'pageStyles' => $styles, 'localFonts' => $this->fonts->hasLocal($theme) ? $this->fonts->preload($theme) : []]);
             }
             if (!isset($body['expectedVersion']) || !is_int($body['expectedVersion']) || $body['expectedVersion'] < 0) {
                 throw new \InvalidArgumentException();
@@ -536,6 +550,9 @@ final class EditorController extends AbstractController
             return $this->json(['error' => 'Inzwischen wurde ein neuerer Stand gespeichert. Deine Änderungen bleiben im Editor. Lade sie als JSON herunter, bevor du den aktuellen Serverstand lädst.', 'conflict' => true], 409);
         } catch (InvalidDocument $e) {
             return $this->json(['error' => 'Bitte prüfe die Inhalte: '.$e->getMessage()], 422);
+        } catch (InvalidPage $e) {
+            // Etwa eine übersetzte Adresse, die eine andere Seite schon hat.
+            return $this->json(['error' => $e->getMessage()], 422);
         } catch (\JsonException|\InvalidArgumentException) {
             return $this->json(['error' => 'Die Anfrage enthält kein gültiges Seitendokument oder keine gültige Version.'], 422);
         }
@@ -549,13 +566,16 @@ final class EditorController extends AbstractController
      *
      * @return array<string, array>
      */
-    private function previewForms(array $documents, array $page): array
+    private function previewForms(array $documents, array $page, ?string $language = null): array
     {
         $states = [];
-        $walk = function (array $blocks) use (&$walk, &$states, $page): void {
+        $walk = function (array $blocks) use (&$walk, &$states, $page, $language): void {
             foreach ($blocks as $block) {
                 if ('form' === ($block['type'] ?? null) && '' !== ($block['props']['form'] ?? '')) {
                     $form = $this->forms->findBySlug((string) $block['props']['form']);
+                    if (null !== $form && null !== $language) {
+                        $form = FormRepository::localise($form, $language);
+                    }
                     $states[$block['id']] = ['form' => $form, 'sent' => false, 'errors' => [], 'values' => [], 'optionImages' => [], 'blockId' => $block['id'], 'page' => $page, 'issued' => 0, 'issuedSignature' => '', 'turnstileKey' => ''];
                 }
                 $walk($block['children'] ?? []);
@@ -575,6 +595,15 @@ final class EditorController extends AbstractController
 
     private function payload(array $page): array
     {
-        return ['document' => $page['document'], 'version' => $page['version'], 'revisionId' => $page['draft_revision_id'], 'publishedRevisionId' => $page['published_revision_id'], 'csrfToken' => $this->csrf->getToken('editor')->getValue(), 'plugins' => $this->plugins->forEditor(), 'presets' => $this->plugins->presetsForEditor()];
+        return ['document' => $page['document'], 'version' => $page['version'], 'revisionId' => $page['draft_revision_id'], 'publishedRevisionId' => $page['published_revision_id'], 'csrfToken' => $this->csrf->getToken('editor')->getValue(), 'plugins' => $this->plugins->forEditor(), 'presets' => $this->plugins->presetsForEditor(),
+            // Für den Sprachumschalter (ADR 111). Ohne weitere Sprache leer - dann gibt es ihn nicht.
+            'languages' => [
+                'main' => $this->languages->describe($this->languages->main()),
+                'extra' => array_map(fn (string $code): array => $this->languages->describe($code), $this->languages->extra()),
+                'slug' => $page['slug'],
+                'home' => $page['path'] === $this->siteSettings->homePath(),
+                'published' => [] === $this->languages->extra() ? [] : $this->pages->translatedPaths($page['id']),
+            ],
+        ];
     }
 }