Is Kama Sutra a book on sex or a guideline for Hindus how to perform sex; like Gita, a spiritual book?
If Kama Sutra is blindly accepted and believed, then it shows that Indians had knowledge about group sex and swinging very much earlier than West.
Does it have English or Tamil translation?
Well it depends on how you would want to view any book.
Any type of knowledge is sacred and you can consider sex as spiritual too cos the feel good hormones are released when the human mind is relaxed whatever the activity is..whether its meditation or even a physical act of the close kind.
In copulation the human mind is totally focused on self gratification and the partner/spouse is merely an instrumental cause...even though some swear its Deiviga!
Now if this is understood one can totally realize that life is a very personal journey for self fulfillment and then one can choose to focus on God or a Higher Entity more efficiently.
One has to grow thru every stage in life..after all even Dharma condones the 4 stages of life e finally leading to Sanyas.
Now coming to Indians had knowledge about sex as you had stated there is nothing to be surprised as Indians have covered all topics in the past right from sex to astronomy.
But its just at times Indians have a tendency to act prudish and down play their sexuality when their body endocrine system could be having a Tsunami of lashing Testosterone.
Now coming to Kama Sutra having an English or Tamil translation as you have asked..my answer is "Yes there is"
But at the same time I cant help wondering.."what were you doing all these years that you have not read the Kama Sutra?"
Go get a copy today..you can find it in any reputed book store in India.
Please do not follow the Kama Sutra "blindly"..why do you want to keep your eyes closed?.....keep your eyes open and you might start to wonder why India had not won a Gold medal in gymnastics at the Olympics.
To follow every illustration there one has to be a master contortionist.
But whatever said and done I feel the Kama Sutra still has many shades of grey left unexplored..may be someone could print a new upgraded version.