Using this option with value ``false`` was deprecated in Symfony 4.1 and it

  will throw an exception in Symfony 5.0. Use ``true`` instead.

If true, the:phpmethod:`Locale::canonicalize` method will be applied before checking

the validity of the given locale (e.g. ``FR-fr.utf8`` is transformed into ``fr_FR``

).

If ``true``, the:phpmethod:`Locale::canonicalize` method will be applied before checking

the validity of the given locale (e.g. ``FR-fr.utf8`` is transformed into ``fr_FR``).

.. _`ICU format locale IDs`:http://userguide.icu-project.org/locale

.. _`ISO 639-1`:https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes