Backend language selector don't work

Hi,
I have read all the support forum topics and I see there are more people with my same problem and nothing to resolve it… also if I have translated the “/translation/backend/it.php” file and I have selected the “Italian (Italiano)” option on the dropdown menu (admin control panel side) the language does not change and remains in English… also if i select other language (like german language because it’s translated).
I have try to rename my “it.php” file in “en.php” and the translation work perfectly… also with the frontend all work with the shortcode “[dopbs lang=it]”.
Can you check the problem with this selector in backend side?
Thank you for your help and time.
Luigi

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