(NDA) SSB entirely in English or can one use Hindi?

Is the (NDA) SSB entirely in English or can one use Hindi?
You can go for it in either language. But since you would be expected to command troops and lead in varied scenarios too.
For, today the Indian Army not only adopts a defensive role but also a heavily contributive outlook in international arena.
It is an active contributor of troops to UN peacekeeping forces and also the international naval security.
Therefore, a working knowledge of English would be great to possess.

And now, the tips.
Learn to speak good communication standard English.
Learn basic current affairs.
Learn to dress according to occasion and as a gentleman.
Learn to be a good listener and try to voice your opinions after measured thinking and good bit of mental processing.
Try to research about what you might encounter in your SSB.
Think about every aspect of your life and create a mindset for yourself where you are clear about every decision that you have taken and its justification.
Practice extempore and sentence formation.
Practice Creative writing.
Be definite and decisive about your qualities and abilities.
Do not brag and be respectful about your deeds and those of others.
Justify every answer and every aspect of your life with proper reasons.
Talk about what you know and what you have learnt.
Practice running and jumping and squats and the exercises such as tiger jump, monkey crawl and rope climbing.
Learn which service branch you are interested in and all about its arms and equipment used.
Get to know the ranks and the promotions of your desired service and also be informed about the latest world level upgrades and innovations in the weaponry and ordinance frequently used in that branch.
Be clear about basics of all your subjects studied in school and college.