Writing a Hindi caption is as easy as you can type Hindi texts on your phone while texting someone.
All you need to do is go to your Settings option.
Choose the language option and you will find that English has been selected as the primary one and there will be another option to add any other language as per your wish.
Select Hindi from the drop down menu.
So, from then onwards your Google keyboard will provide you with both Hindi and English fonts option.
While writing a caption you can switch to Hindi and make wonders. Happy Instagramming!!!