which computer language will be useful for a doctor?

If you become a doctor, then I wouldn't have thought that you'll have time to write your own software. You'll have to buy what you need.

If you intend to set up your own practice as a 'general practitioner' then you'll need to look at practice management software which will manage your appointments, keep patient records etc.

However, if you become a hospital doctor, then the hospital will probably have its own IT department which buys whatever is needed.