If a pharmacy does not have an interpreter
but the pharmacist is willing to communicate
with back and forth notes, is it a violation
of ADA?

Hard to say. ADA says that businesses must
take steps to communicate with deaf customers.

If the deaf customer is uncomfortable with
notes and wants an interpeter, the pharmacist
may be obligated to find one.

But if deaf customer accepts
notes and does not require an interpreter
then there is no ADA violation!