minor #10122 Update translator fallback example to include ICU parents (thewilkybarkid, javiereguiluz)

This PR was merged into the master branch.

Discussion
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Update translator fallback example to include ICU parents

Changes the example to show symfony/symfony#28070.

Commits
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7ccf603 Reworded and added the versionadded directive
54631df Update translator fallback example to include ICU parents

Author: javiereguiluz

components/translation.rst

@@ -162,16 +162,24 @@ Fallback Locales
 
 If the message is not located in the catalog of the specific locale, the
 translator will look into the catalog of one or more fallback locales. For
-example, assume you're trying to translate into the ``fr_FR`` locale:
+example, assume you're trying to translate into the ``es_AR`` locale:
 
-#. First, the translator looks for the translation in the ``fr_FR`` locale;
+#. First, the translator looks for the translation in the ``es_AR``
+   (Argentinean Spanish) locale;
 
-#. If it wasn't found, the translator looks for the translation in the ``fr``
-   locale;
+#. If it wasn't found, the translator looks for the translation in the parent
+   locale, which is automatically defined only for some locales. In this
+   example, the parent locale is ``es_419`` (Latin American Spanish);
+
+#. If it wasn't found, the translator looks for the translation in the ``es``
+   (Spanish) locale;
 
 #. If the translation still isn't found, the translator uses the one or more
    fallback locales set explicitly on the translator.
 
+.. versionadded:: 4.2
+    The use of parent locales was introduced in Symfony 4.2.
+
 For (3), the fallback locales can be set by calling
 :method:`Symfony\\Component\\Translation\\Translator::setFallbackLocales`::