IMHO, there may be some issues with the scenario.
What would be the need to have the existing customer sign on the loan with the relative? That could border on discrimination for national origin if the relative is otherwise qualified.
If the relative agrees, customer can be translator - if not, I would have a concern about privacy issues "forced" by the bank.
Also - if the loan goes past due, what is the bank going to say to the customer/how would they collect?
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