The process is when you listen to sounds ,then only you vl b able to speak ,that should happen with in developmental age (with in 5 to 7 years of age). Now it's late but you can go for hearing
check up (audiometry ,BERA test) then according to the loss audiologist
will suggest you whether to go for hearing aids or cochlear implant
.Keep in mind auditory training is a must after any machine or implant in this case. I request you when you see person like this send them to doctors in early age, do not wait for long time.