Sorry for being so quiet for so long. I'm back with a new present for you: How to load global language file from your Joomla! site in any of your custom extensions. Are you a Joomla! extension developer? You might have had, just like me, that same problem when coding your extension.
How to load the language file fr-FR.ini oren-GB.ini found there: JPATH_ADMINISTRATOR/language/en-GB/en-GB.ini JPATH_ADMINISTRATOR/language/fr-FR/fr-FR.ini or JPATH_SITE/language/en-GB/en-GB.ini JPATH_SITE/language/fr-FR/fr-FR.ini In your extensions and force usage of thoses files, in order to, for example, display correctly translated buttons in a toolbar (the same that is in admin panel on Joomla! frontend).For those of you who are interested, here is the code the force the loading of global language coming from Joomla! backend:
// Force loading of backend global language file
$language = Factory::getLanguage();