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/PartialController.php

@@ -6,10 +6,12 @@ use App\Content\CustomCode;
 use App\Content\DocumentValidator;
 use App\Content\FontLibrary;
 use App\Content\FormRepository;
+use App\Content\Languages;
 use App\Content\MenuRepository;
 use App\Content\PartialRepository;
 use App\Content\StyleCompiler;
 use App\Content\Theme;
+use App\Content\Translations;
 use App\Domain\InvalidDocument;
 use App\Domain\InvalidPage;
 use App\Domain\StaleWrite;
@@ -42,6 +44,7 @@ final class PartialController extends AbstractController
         private CsrfTokenManagerInterface $csrf,
         private PluginRegistry $plugins,
         private FormRepository $forms,
+        private Languages $languages,
     ) {
     }
 
@@ -125,8 +128,8 @@ final class PartialController 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 $this->json(['error' => 'Der Bereich ist zu groß (maximal 256 KiB Inhalt).'], 413);
+        if (strlen($request->getContent()) > 1100000) {
+            return $this->json(['error' => 'Der Bereich ist zu groß (maximal 256 KiB Inhalt, mit Übersetzungen 1 MiB).'], 413);
         }
         $partial = $this->partial($id);
         try {
@@ -137,8 +140,9 @@ final class PartialController extends AbstractController
             }
             if ('admin_partial_preview' === $request->attributes->get('_route')) {
                 $this->validator->validate($document, false, true);
+                $language = $body['language'] ?? null;
 
-                return $this->renderPreview($partial, $document);
+                return $this->renderPreview($partial, $document, $request, is_string($language) && $this->languages->isExtra($language) ? $language : null);
             }
             if (!isset($body['expectedVersion']) || !is_int($body['expectedVersion'])) {
                 throw new \InvalidArgumentException();
@@ -163,18 +167,25 @@ final class PartialController extends AbstractController
     }
 
     /** The area on its own, in the shell of a page, so the editor preview looks like the result. */
-    private function renderPreview(array $partial, array $document): Response
+    private function renderPreview(array $partial, array $document, Request $request, ?string $language = null): Response
     {
+        // Ein Bereich in einer weiteren Sprache (ADR 111): seine Texte, die seiner Sektionen und
+        // die Menübeschriftungen in dieser Sprache - wie auf einer übersetzten Seite.
+        $localise = static fn (array $doc): array => null === $language ? Translations::strip($doc) : Translations::apply($doc, $language);
+        $document = $localise($document);
+        $locale = $language ?? $this->languages->main();
+        $request->attributes->set('kant_locale', $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()));
         $theme = $this->theme->load();
         $navigation = [];
         foreach ($this->menus->all() as $slot => $menu) {
-            $navigation[$slot] = $this->menus->resolve($menu['items'], '');
+            $navigation[$slot] = $this->menus->resolve($menu['items'], '', language: $language);
         }
         $sections = [];
         foreach ($this->partials->referencedSlugs($document) as $slug) {
             $section = $this->partials->resolveSection($slug);
             if (null !== $section) {
-                $sections[$slug] = $section['document'];
+                $sections[$slug] = $localise($section['document']);
             }
         }
 
@@ -184,10 +195,13 @@ final class PartialController extends AbstractController
             $styles .= $this->styles->compileDocument($section).$this->code->compileDocument($section);
         }
         $forms = [];
-        $walk = function (array $blocks) use (&$walk, &$forms): void {
+        $walk = function (array $blocks) use (&$walk, &$forms, $language): void {
             foreach ($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);
+                    }
                     $forms[$block['id']] = ['form' => $form, 'sent' => false, 'errors' => [], 'values' => [], 'optionImages' => [], 'blockId' => $block['id'], 'page' => ['path' => ''], 'issued' => 0, 'issuedSignature' => '', 'turnstileKey' => ''];
                     if (null !== $form) {
                         $styles .= $this->forms->css($form, $theme);
@@ -202,7 +216,7 @@ final class PartialController extends AbstractController
         }
 
         return $this->render('page.html.twig', [
-            'page' => ['locale' => 'de', 'path' => '', 'type' => 'page', 'slug' => '', 'document' => $document],
+            'page' => ['locale' => $locale, 'path' => '', 'type' => 'page', 'slug' => '', 'document' => $document],
             'canonical' => '',
             'editing' => true,
             'navigation' => $navigation,
@@ -232,6 +246,12 @@ final class PartialController extends AbstractController
             'csrfToken' => $this->csrf->getToken('editor')->getValue(),
             'plugins' => $this->plugins->forEditor(),
             'presets' => $this->plugins->presetsForEditor(),
+            // Kopf, Fuß und Sektionen werden wie Seiten übersetzt, nur ohne Adresse und Suchtitel.
+            'languages' => [
+                'main' => $this->languages->describe($this->languages->main()),
+                'extra' => array_map(fn (string $code): array => $this->languages->describe($code), $this->languages->extra()),
+                'area' => true,
+            ],
         ];
     }