[5.x] Fix localized error messages on forms when previous URL is incorrect

src/Forms/Tags.php

@@ -91,7 +91,7 @@ public function create()
         }
 
         $knownParams = array_merge(static::HANDLE_PARAM, [
-            'redirect', 'error_redirect', 'allow_request_redirect', 'csrf', 'files', 'js',
+            'redirect', 'error_redirect', 'allow_request_redirect', 'csrf', 'files', 'js', 'original_url',
         ]);
 
         $action = $this->params->get('action', $form->actionUrl());
@@ -104,7 +104,9 @@ public function create()
         }
         $attrs = $this->runHooks('attrs', ['attrs' => $attrs, 'data' => $data])['attrs'];
 
-        $params = [];
+        $params = [
+            'original_url' => request()->url(),
+        ];
 
         if ($redirect = $this->getRedirectUrl()) {
             $params['redirect'] = $this->parseRedirect($redirect);

src/Http/Requests/FrontendFormRequest.php

@@ -120,7 +120,7 @@ public function validateResolved()
         // If this was submitted from a front-end form, we want to use the appropriate language
         // for the translation messages. If there's no previous url, it was likely submitted
         // directly in a headless format. In that case, we'll just use the default lang.
-        $site = ($previousUrl = session()->previousUrl()) ? Site::findByUrl($previousUrl) : null;
+        $site = ($previousUrl = $this->input('_original_url')) ? Site::findByUrl($previousUrl) : null;
 
         return $this->withLocale($site?->lang(), fn () => parent::validateResolved());
     }

tests/Tags/Form/FormCreateTest.php

@@ -4,11 +4,13 @@
 
 use Illuminate\Http\UploadedFile;
 use Illuminate\Support\Facades\Event;
+use Illuminate\Support\Facades\Request;
 use Illuminate\Support\Facades\Storage;
 use Illuminate\Validation\ValidationException;
 use PHPUnit\Framework\Attributes\Test;
 use Statamic\Facades\AssetContainer;
 use Statamic\Facades\Form;
+use Statamic\Facades\Site;
 use Statamic\Statamic;
 
 class FormCreateTest extends FormTestCase
@@ -53,6 +55,16 @@ public function it_renders_form_with_redirects_to_anchor()
         $this->assertStringContainsString('<input type="hidden" name="_error_redirect" value="http://localhost#form" />', $output);
     }
 
+    #[Test]
+    public function it_renders_original_url()
+    {
+        Request::swap(Request::create('http://localhost/contact'));
+
+        $output = $this->tag('{{ form:contact }}');
+
+        $this->assertStringContainsString('<input type="hidden" name="_original_url" value="http://localhost/contact" />', $output);
+    }
+
     #[Test]
     public function it_dynamically_renders_fields_array()
     {
@@ -804,6 +816,53 @@ public function it_can_render_an_inline_error_when_multiple_rules_fail()
         $this->assertEquals($expectedInline, $inlineErrors[1]);
     }
 
+    #[Test]
+    public function it_uses_original_url_to_localize_error_messages()
+    {
+        trans()->addLines([
+            'validation.required' => 'Das :attribute Feld ist erforderlich.',
+        ], 'de');
+
+        Site::setSites([
+            'default' => [
+                'name' => 'English',
+                'url' => '/',
+                'locale' => 'en_US',
+            ],
+            'german' => [
+                'name' => 'German',
+                'url' => '/de/',
+                'locale' => 'de_DE',
+            ],
+        ]);
+
+        $this->assertEmpty(Form::find('contact')->submissions());
+
+        $this
+            ->post('/!/forms/contact', [
+                '_original_url' => 'http://localhost/de/contact',
+                'email' => '[email protected]',
+                'message' => '',
+            ])
+            ->assertSessionHasErrors(['message'], null, 'form.contact')
+            ->assertLocation('/');
+
+        $this->assertEmpty(Form::find('contact')->submissions());
+
+        $output = $this->tag(<<<'EOT'
+{{ form:contact }}
+    {{ errors }}
+        <p class="error">{{ value }}</p>
+    {{ /errors }}
+    <p class="inline-error">{{ error:name }}</p>
+{{ /form:contact }}
+EOT
+        );
+
+        $this->assertStringContainsString('<p class="error">Das Message Feld ist erforderlich.</p>', $output);
+        $this->assertStringNotContainsString('<p class="error">The Message field is required.</p>', $output);
+    }
+
     #[Test]
     public function it_fetches_form_data()
     {