Formal:
* 祝您今天愉快 (zhù nín jīntiān yúkuài): This is the most common and formal way to say "Have a nice day." It literally translates to "Wish you a pleasant day."
* 祝您一天順利 (zhù nín yītiān shùnlì): This means "Wish you a smooth day." It's a bit more formal than the previous phrase.
Informal:
* 祝你今天开心 (zhù nǐ jīntiān kāixīn): This translates to "Wish you a happy day" and is suitable for friends or family.
* 今天过得愉快 (jīntiān guò de yúkuài): This means "Have a pleasant day" and is a more casual way to say it.
More colloquial:
* 玩得开心 (wán de kāixīn): This means "Have fun," and is a casual way to say goodbye.
Note: The tone of voice is important. If you use a formal phrase with a casual tone, it might sound strange.
The best way to choose the appropriate phrase is to consider the context and your relationship with the person you're speaking to.