没有西瓜的夏天叫不完整
[méi yŏu xī guā de xià tiān jiào bù wán zhĕng]
This translates to 'A Summer Without Watermelon Is Incomplete.' A fun and lighthearted sentiment indicating joy and fondness for summer and its quintessential experiences like eating watermelons, signifying a belief in enjoying simple pleasures and nostalgia.