diff --git a/src/Symfony/Component/Routing/Loader/AnnotationClassLoader.php b/src/Symfony/Component/Routing/Loader/AnnotationClassLoader.php
index 6390a79f5811..ce61032ac341 100644
--- a/src/Symfony/Component/Routing/Loader/AnnotationClassLoader.php
+++ b/src/Symfony/Component/Routing/Loader/AnnotationClassLoader.php
@@ -18,6 +18,7 @@
 use Symfony\Component\Routing\Annotation\Route as RouteAnnotation;
 use Symfony\Component\Routing\Route;
 use Symfony\Component\Routing\RouteCollection;
+use Symfony\Component\Routing\RouteCompiler;
 
 /**
  * AnnotationClassLoader loads routing information from a PHP class and its methods.
@@ -211,6 +212,7 @@ protected function addRoute(RouteCollection $collection, $annot, $globals, \Refl
             $this->configureRoute($route, $class, $method, $annot);
             if (0 !== $locale) {
                 $route->setDefault('_locale', $locale);
+                $route->setRequirement('_locale', preg_quote($locale, RouteCompiler::REGEX_DELIMITER));
                 $route->setDefault('_canonical_route', $name);
                 $collection->add($name.'.'.$locale, $route);
             } else {
diff --git a/src/Symfony/Component/Routing/Loader/Configurator/Traits/AddTrait.php b/src/Symfony/Component/Routing/Loader/Configurator/Traits/AddTrait.php
index 085fde4bc9f4..84899aa2e27f 100644
--- a/src/Symfony/Component/Routing/Loader/Configurator/Traits/AddTrait.php
+++ b/src/Symfony/Component/Routing/Loader/Configurator/Traits/AddTrait.php
@@ -15,6 +15,7 @@
 use Symfony\Component\Routing\Loader\Configurator\RouteConfigurator;
 use Symfony\Component\Routing\Route;
 use Symfony\Component\Routing\RouteCollection;
+use Symfony\Component\Routing\RouteCompiler;
 
 trait AddTrait
 {
@@ -67,6 +68,7 @@ final public function add(string $name, $path): RouteConfigurator
             $routes->add($name.'.'.$locale, $route = $this->createRoute($path));
             $this->collection->add($this->name.$name.'.'.$locale, $route);
             $route->setDefault('_locale', $locale);
+            $route->setRequirement('_locale', preg_quote($locale, RouteCompiler::REGEX_DELIMITER));
             $route->setDefault('_canonical_route', $this->name.$name);
         }
 
diff --git a/src/Symfony/Component/Routing/Loader/XmlFileLoader.php b/src/Symfony/Component/Routing/Loader/XmlFileLoader.php
index dc208f28e16c..da8f34b293c1 100644
--- a/src/Symfony/Component/Routing/Loader/XmlFileLoader.php
+++ b/src/Symfony/Component/Routing/Loader/XmlFileLoader.php
@@ -16,6 +16,7 @@
 use Symfony\Component\Config\Util\XmlUtils;
 use Symfony\Component\Routing\Route;
 use Symfony\Component\Routing\RouteCollection;
+use Symfony\Component\Routing\RouteCompiler;
 
 /**
  * XmlFileLoader loads XML routing files.
@@ -129,6 +130,7 @@ protected function parseRoute(RouteCollection $collection, \DOMElement $node, $p
             foreach ($paths as $locale => $p) {
                 $defaults['_locale'] = $locale;
                 $defaults['_canonical_route'] = $id;
+                $requirements['_locale'] = preg_quote($locale, RouteCompiler::REGEX_DELIMITER);
                 $route = new Route($p, $defaults, $requirements, $options, $node->getAttribute('host'), $schemes, $methods, $condition);
                 $collection->add($id.'.'.$locale, $route);
             }
diff --git a/src/Symfony/Component/Routing/Loader/YamlFileLoader.php b/src/Symfony/Component/Routing/Loader/YamlFileLoader.php
index 0de36c93b2e5..868da9bd30b4 100644
--- a/src/Symfony/Component/Routing/Loader/YamlFileLoader.php
+++ b/src/Symfony/Component/Routing/Loader/YamlFileLoader.php
@@ -15,6 +15,7 @@
 use Symfony\Component\Config\Resource\FileResource;
 use Symfony\Component\Routing\Route;
 use Symfony\Component\Routing\RouteCollection;
+use Symfony\Component\Routing\RouteCompiler;
 use Symfony\Component\Yaml\Exception\ParseException;
 use Symfony\Component\Yaml\Parser as YamlParser;
 use Symfony\Component\Yaml\Yaml;
@@ -140,6 +141,7 @@ protected function parseRoute(RouteCollection $collection, $name, array $config,
             foreach ($config['path'] as $locale => $path) {
                 $localizedRoute = clone $route;
                 $localizedRoute->setDefault('_locale', $locale);
+                $localizedRoute->setRequirement('_locale', preg_quote($locale, RouteCompiler::REGEX_DELIMITER));
                 $localizedRoute->setDefault('_canonical_route', $name);
                 $localizedRoute->setPath($path);
                 $collection->add($name.'.'.$locale, $localizedRoute);
diff --git a/src/Symfony/Component/Routing/Tests/Loader/AnnotationClassLoaderTest.php b/src/Symfony/Component/Routing/Tests/Loader/AnnotationClassLoaderTest.php
index 441900775114..c8794e10b674 100644
--- a/src/Symfony/Component/Routing/Tests/Loader/AnnotationClassLoaderTest.php
+++ b/src/Symfony/Component/Routing/Tests/Loader/AnnotationClassLoaderTest.php
@@ -125,6 +125,9 @@ public function testLocalizedPathRoutes()
         $this->assertCount(2, $routes);
         $this->assertEquals('/path', $routes->get('action.en')->getPath());
         $this->assertEquals('/pad', $routes->get('action.nl')->getPath());
+
+        $this->assertEquals('nl', $routes->get('action.nl')->getRequirement('_locale'));
+        $this->assertEquals('en', $routes->get('action.en')->getRequirement('_locale'));
     }
 
     public function testLocalizedPathRoutesWithExplicitPathPropety()
diff --git a/src/Symfony/Component/Routing/Tests/Loader/PhpFileLoaderTest.php b/src/Symfony/Component/Routing/Tests/Loader/PhpFileLoaderTest.php
index 71f9df15470a..789848c66021 100644
--- a/src/Symfony/Component/Routing/Tests/Loader/PhpFileLoaderTest.php
+++ b/src/Symfony/Component/Routing/Tests/Loader/PhpFileLoaderTest.php
@@ -229,11 +229,11 @@ public function testRoutingI18nConfigurator()
 
         $expectedCollection = new RouteCollection();
 
-        $expectedCollection->add('foo.en', (new Route('/glish/foo'))->setDefaults(['_locale' => 'en', '_canonical_route' => 'foo']));
-        $expectedCollection->add('bar.en', (new Route('/glish/bar'))->setDefaults(['_locale' => 'en', '_canonical_route' => 'bar']));
-        $expectedCollection->add('baz.en', (new Route('/baz'))->setDefaults(['_locale' => 'en', '_canonical_route' => 'baz']));
-        $expectedCollection->add('c_foo.fr', (new Route('/ench/pub/foo'))->setDefaults(['_locale' => 'fr', '_canonical_route' => 'c_foo']));
-        $expectedCollection->add('c_bar.fr', (new Route('/ench/pub/bar'))->setDefaults(['_locale' => 'fr', '_canonical_route' => 'c_bar']));
+        $expectedCollection->add('foo.en', (new Route('/glish/foo'))->setDefaults(['_locale' => 'en', '_canonical_route' => 'foo'])->setRequirement('_locale', 'en'));
+        $expectedCollection->add('bar.en', (new Route('/glish/bar'))->setDefaults(['_locale' => 'en', '_canonical_route' => 'bar'])->setRequirement('_locale', 'en'));
+        $expectedCollection->add('baz.en', (new Route('/baz'))->setDefaults(['_locale' => 'en', '_canonical_route' => 'baz'])->setRequirement('_locale', 'en'));
+        $expectedCollection->add('c_foo.fr', (new Route('/ench/pub/foo'))->setDefaults(['_locale' => 'fr', '_canonical_route' => 'c_foo'])->setRequirement('_locale', 'fr'));
+        $expectedCollection->add('c_bar.fr', (new Route('/ench/pub/bar'))->setDefaults(['_locale' => 'fr', '_canonical_route' => 'c_bar'])->setRequirement('_locale', 'fr'));
 
         $expectedCollection->addResource(new FileResource(realpath(__DIR__.'/../Fixtures/php_dsl_sub_i18n.php')));
         $expectedCollection->addResource(new FileResource(realpath(__DIR__.'/../Fixtures/php_dsl_i18n.php')));
diff --git a/src/Symfony/Component/Routing/Tests/Loader/XmlFileLoaderTest.php b/src/Symfony/Component/Routing/Tests/Loader/XmlFileLoaderTest.php
index e27149f93125..66d54fc985c4 100644
--- a/src/Symfony/Component/Routing/Tests/Loader/XmlFileLoaderTest.php
+++ b/src/Symfony/Component/Routing/Tests/Loader/XmlFileLoaderTest.php
@@ -185,6 +185,9 @@ public function testLocalizedImports()
 
         $this->assertEquals('/le-prefix/le-suffix', $routeCollection->get('imported.fr')->getPath());
         $this->assertEquals('/the-prefix/suffix', $routeCollection->get('imported.en')->getPath());
+
+        $this->assertEquals('fr', $routeCollection->get('imported.fr')->getRequirement('_locale'));
+        $this->assertEquals('en', $routeCollection->get('imported.en')->getRequirement('_locale'));
     }
 
     public function testLocalizedImportsOfNotLocalizedRoutes()
diff --git a/src/Symfony/Component/Routing/Tests/Loader/YamlFileLoaderTest.php b/src/Symfony/Component/Routing/Tests/Loader/YamlFileLoaderTest.php
index caad0aa978ea..52c21c287fcf 100644
--- a/src/Symfony/Component/Routing/Tests/Loader/YamlFileLoaderTest.php
+++ b/src/Symfony/Component/Routing/Tests/Loader/YamlFileLoaderTest.php
@@ -321,6 +321,9 @@ public function testImportingRoutesWithLocales()
         $this->assertCount(2, $routes);
         $this->assertEquals('/nl/voorbeeld', $routes->get('imported.nl')->getPath());
         $this->assertEquals('/en/example', $routes->get('imported.en')->getPath());
+
+        $this->assertEquals('nl', $routes->get('imported.nl')->getRequirement('_locale'));
+        $this->assertEquals('en', $routes->get('imported.en')->getRequirement('_locale'));
     }
 
     public function testImportingNonLocalizedRoutesWithLocales()