Exactly, each field group is a post type and the builder saves all data to the database. Then use the function to register meta boxes and custom fields based on that data. Loco might not scan the text from there. You will need to use the PHP code to register meta boxes and fields to translate by Loco Translate.
Thanks for your response
in the meantime i posted the question on WPML plugin's page, and here is their answer:
Andrés replied to your question:
"Hello there, It would depend on how your plugin is storing that information. For a multilingual ready plugin, WPML should be able to read and translate those labels for the backend. You would need just to analyse your plugin and translate those strings using WPML String Translation Regards"
Reminder - your question was:
"Thanks for your replay, but my question was about the admin area, please forward my question to technical team, because it's an advanced topic, when i change the language on admin area ( the backend ) i need my metabox custom fields """LABELS""" to be translated, not for frontend, i need translations for different admins with different languages ! i hope you can understand me, and i can't find this specific question on the forum, everythig is about the custom fields contents but not labels ! these labels are stored on the database. thanks again"