If you want to express a happy and casual New Year's greeting in Chinese, try using the phrase Xin nian huale, which literally means 'have a happy new year' in Mandarin. You can also use Ni hao, Xin Nian hua le!, which is a more informal way of saying it. Both phrases are widely understood and appreciated by the Chinese people, and are a great way to show your respect and goodwill during this time of celebration.