I have done the following checklist:
Though in my twig template file,
{{ 'message'|trans }}
never translates.
Where can I look next in order to make translations work?
Is there any chance that Doctrine Translatable Extension that I am using generates some kind of conflicts?
Have you enabled the Translator service in your config file?
framework:
translator: { fallbacks: en }
The language catalogue is created in your cache folder irrespective of whether your translator is enabled or not.
Did you try translating in your controller?
$trans = $this->get('translator')->trans('message');