Hi,
unfortunately Joomla store plugin language files in administrator folder, so you will find language constant only if you search for "Administrator" language (note: after found the language constant you need to add it into "Site" language)
Anyway, you can find all constants in file /administrator/language/en-GB/en-GB.plg_jsn_gdpr.ini.....here the content:
PLG_JSN_DELETEACCOUNT_TAB="Delete Account"
PLG_JSN_DELETEACCOUNT_LABEL="Delete Your Account"
PLG_JSN_DELETEACCOUNT_DESC=""
PLG_JSN_DELETEACCOUNT_CHECK="Yes, I want to delete my account"
PLG_JSN_DELETEACCOUNT_INFO="Are you sure you want to delete your account? <br /> After deleting account you won't be able to recover it."
PLG_JSN_DELETEACCOUNT_BUTTON="Delete my account, this action will not be reversible!!"
PLG_JSN_DELETEACCOUNT_JSALERT="Are you sure?"
PLG_JSN_DELETEACCOUNT_ACCOUNTDELETED="Your information has been deleted correctly"
PLG_JSN_DELETEACCOUNT_ACCOUNTBLOCKED="You account has been blocked and you are no more able to make a login, in the next hours one of our administrators will delete all your data from our systems"
PLG_JSN_DELETEACCOUNT_ERROR="Error, please contact system administrator"
PLG_JSN_DELETEACCOUNT_EMAIL_SUBJECT="Request for deleting account"
PLG_JSN_DELETEACCOUNT_EMAIL_BODY="Hi, \n\n User %s (id : %s) has requested to delete/block his/her account.\n\n This is an automated generated email. Please do not respond to it."
PLG_JSN_DELETEACCOUNT_ACTION="Action"
PLG_JSN_DELETEACCOUNT_ACTION_DESC="Choose which action to take when user request to delete own informations."
PLG_JSN_DELETEACCOUNT_ACTION_BLOCK="Block User"
PLG_JSN_DELETEACCOUNT_ACTION_DELETE="Delete User"