minor #14003 [String] Fix missing locale in slugger substitution map (moltam)

This PR was merged into the 5.1 branch.

Discussion
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[String] Fix missing locale in slugger substitution map

The locale was missing from the substitution map, so the example code did not replace the symbols as the comment stated.

Commits
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ae0b34e [String] Fix missing locale in slugger substitution map

Author: xabbuh

components/string.rst

@@ -469,7 +469,7 @@ that only includes safe ASCII characters::
     // $slug = 'Workspace-settings'
 
     // you can also pass an array with additional character substitutions
-    $slugger = new AsciiSlugger('en', ['%' => 'percent', '€' => 'euro']);
+    $slugger = new AsciiSlugger('en', ['en' => ['%' => 'percent', '€' => 'euro']]);
     $slug = $slugger->slug('10% or 5€');
     // $slug = '10-percent-or-5-euro'