Yes, Nokia 1 does support the Tamil language.
No. Nokia 1 does not have the front camera flash.
Nokia 1 is not completely metal body. It has metal chassis frame and the housing is made of polycarbonate material.
Nokia 1 has IP52 certification. It is not exactly waterproof but it does have drip protection.
The Nokia 1 is an inexpensive Android smartphone, and as you can tell from the Nokia 1 review, you very much get what you pay for.