parameters:
    darvin_utils.intl.twig_extension.class: Twig_Extensions_Extension_Intl

services:
    darvin_utils.intl.twig_extension:
        class: %darvin_utils.intl.twig_extension.class%
        tags:
            - { name: twig.extension }

parameters:
    darvin_utils.intl.twig_extension.class: Twig_Extensions_Extension_Intl

services:
    darvin_utils.intl.twig_extension:
        class:  %darvin_utils.intl.twig_extension.class%
        public: false
        tags:
            - { name: twig.extension }

Make Intl Twig extension private.
Make Intl Twig extension private.
