It's used in the United States. It's reasonably common in the United States. I think it's more common in the UK. An awful lot of supposed US/British differences are just differences in frequency of use, and within the United States there can be regional differences, too. You don't get any more American than the songwriter Irving Berlin, and I thought of his song "It's a Lovely Day Today." And one by US songwriter Dorothy Fields, "You're lovely to look at, delightful to know, and heaven to kiss." And by US songwriter Cole Porter, "It's delightful, it's delicious, it's de-lovely." For a completely up-to-date example, a US politician, replying to unkind things another politician said about his wife, tweeted "Real men don't attack women. Your wife is lovely, and Heidi is the love of my life." "Cosmopolitan" magazine writes in conversational English, using the voice of young US women. I find that the magazine has said "If you're looking for some inspiration, here are 16 ways to use greenery to make your home look lovely" and "16 lovely DIY wedding ideas for crafty brides" and "Here's the Lovely New Video for Leona Lewis's 'Thunder'" and "Leave a lovely comment instead of just mindlessly liking a Facebook or Instagram post." "Lovely" tends to be used to give a compliment in a very polite way.

Australians say it too :)

It's definitely more common in Britain, but it's still used in the US. The last one is pretty commonplace in the US.

It sounds more like a British word