I agree with Mike, заткнись- the best match. But if you want more informal ))) : закрой рот! закройся! завали хлебало! But I strongly recommend not to use it :) Just for your collection

'shut up' in Russian - заткнись

I like better the variant of russian shut the fuck up sounds great If to a man "Заткнулся нахуй!" if to a woman "Заткнулась нахуй!"

shut up in italian is "stai zitto!" or just "zitto!"... you can also say "taci!" but is less colloquial. byeee,fede

умолкни / молчи (=keep silence) тихо (=quiet!) тсс! (=hush) закрой рот (=close your mouth) But i think it's all too rude to use with recently familiar people