Documented the slugger

Author: javiereguiluz

components/string.rst

@@ -394,7 +394,55 @@ letter A with ring above"*) or a sequence of two code points (``U+0061`` =
 Slugger
 -------
 
-Document https://github.com/symfony/symfony-docs/issues/12404
+In some contexts, such as URLs and file/directory names, it's not safe to use
+any Unicode character. A *slugger* transforms a given string into another string
+that only includes safe ASCII characters::
+
+    use Symfony\Component\String\Slugger\AsciiSlugger;
+
+    $slugger = new AsciiSlugger();
+    $slug = $slugger->slug('Wôrķšƥáçè ~~sèťtïñğš~~');
+    // $slug = 'Workspace-settings'
+
+The separator between words is a dash (``-``) by default, but you can define
+another separator as the second argument::
+
+    $slug = $slugger->slug('Wôrķšƥáçè ~~sèťtïñğš~~', '/');
+    // $slug = 'Workspace/settings'
+
+The slugger transliterates the original string into the Latin script before
+applying the other transformations. The locale of the original string is
+detected automatically, but you can define it explicitly::
+
+    // this tells the slugger to transliterate from Korean language
+    $slugger = new AsciiSlugger('ko');
+
+    // you can override the locale as the third optional parameter of slug()
+    $slug = $slugger->slug('...', '-', 'fa');
+
+In a Symfony application, you don't need to create the slugger yourself. Thanks
+to :doc:`service autowiring </service_container/autowiring>`, you can inject a
+slugger by type-hinting a service constructor argument with the
+:class:`Symfony\\Component\\String\\Slugger\\SluggerInterface`. The locale of
+the injected slugger is the value of the application's
+:ref:`default_locale option <config-framework-default_locale>`::
+
+    use Symfony\Component\String\Slugger\SluggerInterface;
+
+    class MyService
+    {
+        private $slugger;
+
+        public function __construct(SluggerInterface $slugger)
+        {
+            $this->slugger = $slugger;
+        }
+
+        public function someMethod()
+        {
+            $slug = $slugger->slug('...');
+        }
+    }
 
 .. _`ASCII`: https://en.wikipedia.org/wiki/ASCII
 .. _`Unicode`: https://en.wikipedia.org/wiki/Unicode