Fix error pages in multilang

Fixes #4834

src/Cms/Language.php

@@ -8,6 +8,7 @@
 use Kirby\Exception\LogicException;
 use Kirby\Exception\PermissionException;
 use Kirby\Filesystem\F;
+use Kirby\Toolkit\A;
 use Kirby\Toolkit\Locale;
 use Kirby\Toolkit\Str;
 use Throwable;
@@ -213,7 +214,7 @@ public static function create(array $props): static
 	 */
 	public function delete(): bool
 	{
-		$kirby = App::instance();
+		$kirby = $this->kirby();
 		$user  = $kirby->user();
 		$code  = $this->code();
 
@@ -382,7 +383,20 @@ public function pattern(): string
 		$path = $this->path();
 
 		if (empty($path) === true) {
-			return '(:all)';
+			$pattern = '(:all)';
+
+			// match anything except paths that begin with the prefix
+			// of any other language
+			$languages = $this->kirby()->languages()->not($this)->values(
+				fn ($language) => $language->path()
+			);
+
+			if (count($languages) > 0) {
+				$pattern = '^(?!(?:' . A::join($languages, '|') . ')\/)' . $pattern;
+			}
+
+
+			return $pattern;
 		}
 
 		return $path . '/(:all?)';

tests/Cms/Languages/LanguageTest.php

@@ -556,6 +556,33 @@ public function testPattern($input, $expected)
 		$this->assertSame($expected, $language->pattern());
 	}
 
+	/**
+	 * @covers ::pattern
+	 */
+	public function testPatternWithNoPathPrefixButOtherLanguages()
+	{
+		$app = $this->app->clone([
+			'languages' => [
+				[
+					'code'    => 'en',
+					'name'    => 'English',
+					'default' => true,
+					'url'     => '/'
+				],
+				[
+					'code' => 'de',
+					'name' => 'Deutsch',
+				],
+				[
+					'code' => 'fr',
+					'name' => 'Frances',
+				]
+			]
+		]);
+
+		$this->assertSame('^(?!(?:de|fr)\/)(:all)', $app->language('en')->pattern());
+	}
+
 	/**
 	 * @covers ::root
 	 */