I agree with the speech therapists opinion that their is clear delay and the cause needs to be known before making a decision about whether language and speech will develop or not. As per 4 years is concern, a child's critical learning period for speech and language is 0-7years. Yes, 4years is late. But still if proper therapy is given. Based on the child's disorder improvement can be seen.

Yes4year is quite late for not talking,after 2year if no speech we usually start working for finding the cause of delay

There clearly is a delay in the speech milestones. You may need to visit the speech and occupational therapists to get to know the proper line of intervention for your child. There is a series of assessments that may be required to be done before starting off the therapies.