Venkat, I don’t know how to answer your question. Not only do I not know anything about either of the languages – I am not entirely clear on your family’s logistics. It sounds as though your baby would be separated from you if you sent him to another city for speech therapy. In general, that is not good and should be avoided at all costs. If my interpretation of your living arrangement is incorrect, please forgive me.
Regardless of your geographic situation, it’s unusual to have speech therapy recommended for a child as young as 20 months. There are many children whose later language development turns out to be perfectly normal who have few if any words at that age. I do not know the situation in India, but in this country most speech and language specialists would mainly recommend things for the parents to do with a child as young as your son. Some of those recommendations would be that you read simple books to him daily, use only one language with him (your native tongue, I assume), speak distinctly and slowly to him, point out the names of objects in his everyday environment and do nothing that would increase his anxiety about speaking. Since you have already consulted doctors about his situation, I assume that his hearing has been carefully checked, an essential first step.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.