I have tested this item ✅ successfully on d6b66ca

Surely this was supposed to be handled in the js here

But that JS requires the translation strings to be present before it can use them... and this translated string was not in the page to be used - same as JGLOBAL_WARNCOOKIES

 "joomla.jtext": {
            "JSHOWPASSWORD": "Show Password",
            "JHIDEPASSWORD": "Hide Password",
            "ERROR": "Error",
            "WARNING": "Warning",
            "NOTICE": "Notice",
            "MESSAGE": "Message",
            "JGLOBAL_WARNCOOKIES": "Warning! Cookies must be enabled to access the Administrator Backend.",
            "JLIB_JS_AJAX_ERROR_OTHER": "An error has occurred while fetching the JSON data: HTTP %s status code.",
            "JCLOSE": "Close",
            "JOK": "OK",
            "JOPEN": "Open",
            "JLIB_FORM_CONTAINS_INVALID_FIELDS": "The form cannot be submitted as it's missing required data. <br> Please correct the marked fields and try again.",
            "JLIB_FORM_FIELD_REQUIRED_VALUE": "Please fill in this field",
            "JLIB_FORM_FIELD_REQUIRED_CHECK": "One of the options must be selected",
            "JLIB_FORM_FIELD_INVALID_VALUE": "This value is not valid"
        },

Restarted drone.

I have tested this item ✅ successfully on d6b66ca

I can confirm the error message is translated. But ... what does 'An error has occurred while fetching the JSON data: HTTP 0 status code.' actually mean to the user?

rtc

Merged thanks @PhilETaylor I have added the label and the tag so that should help you geting the shirt right?

Haha I was only (half) joking about the T-Shirt ?