Formal:
* 祝您夏天愉快 (Zhù nín xiàtiān yúkuài): This translates literally to "Wish you a happy summer," and is a polite way to greet someone during the summer months.
* 夏日快乐 (Xiàrì kuàilè): This is another formal way to say "Happy summer," meaning "Happy Summer Day."
Informal:
* 夏天快乐 (Xiàtiān kuàilè): This is a more casual way to say "Happy summer."
* 祝你夏天愉快 (Zhù nǐ xiàtiān yúkuài): This is a less formal version of the first formal option, suitable for friends and family.
You can also use 夏天好 (Xiàtiān hǎo), which is a general greeting for the summer season, similar to saying "Hello" or "Good summer" in English.
The best way to choose the right phrase depends on the situation and your relationship with the person you're speaking to.