Knowledge is power.
Google now started recognising other languages also and we are seeing many adds on Google in Hindi and other regional languages also. So we can search in those languages also and we have to select the language we want and search in that.
But mix up of English and other languages may not be accepted by Google in keywords. If your content is in English and the keywords are in another language Google may not accept I feel.
And is your doubt about Google indexing Hindi words or ISC not allowing direct usage of Hindi/ any other regional language? Being a Platinum member and having been associated with this site for so long, I am sure you must be aware that we accept only English.
'The journey of a thousand miles begins with one step'.
K Mohan @ Moga
'Idhuvum Kadandhu Pogum "
Even this challenging situation would ease