I have just started to review of your bundle to replace nearly dead JMSTranslationBundle (even if I have succeded to make it work in SF4 it does not give any hope for long-term usage).
I have some lines in Symfony4 controller - used to build some breadcrumbs. I have to translate them in controller as they are built with some translateable strings (like shown below "Users" string) and also non-translateable. I am (it seems unfortunately) using 'label' key in breadcrumb array which causes errors in translation:extract Symfony Command.
Code from controller (both lines fail, however 'breadcrumb.users' string is correctly added to the dictionairy):
$params['breadcrumbs'][] = ['label' => $this->get('translator')->trans('breadcrumb.users'), 'route' => 'app_parameters_user_index'];
$params['breadcrumbs'][] = ['label' => $user->getNameAndSurname()];
It seems default extractor looks for "label" field in an array despite the real context (JMSTranslationBundle was smarter in this case).