但願人長久 is a very old Chinese poem. Written by 蘇轼 (Su1 Shi4, 1037 to 1101).
In modern times, it has been sung as a song, made very popular by 鄧麗君 (Teresa Deng), and also sung by 王菲 (Faye Wong). The music is by 梁弘志 (liáng HóngZhì).
Here is the lyrics:
明月幾時有，把酒問青天 不知天上宮闕，今夕是何年 我欲乘風歸去 唯恐琼樓玉宇，高處不勝寒 起舞弄清影，何似在人間 轉朱閣，低綺戶，照無眠 不應有恨，何事偏向別時圓 人有悲歡離合，月有陰晴圓缺 此事古難全，但願人長久，千里共嬋娟
translation by 许渊冲 (Xu Yuanchong) How long will the full moon appear? Wine cup in hand, I ask the sky. I do not know what time of the year It would be tonight in the palace on high. Riding the wind, there I would fly, Yet I'm afraid the crystalline palace would be Too high and cold for me. I rise and dance, with my shadow I play. On high as on earth, would it be as gay? The moon goes round the mansions red Through gauze-draped window soft to shed Her light upon the sleepless bed. Why then when people part, is the oft full and bright? Men have sorrow and joy; they part or meet again; The moon is bright or dim and she may wax or wane. There has been nothing perfect since the olden days. So let us wish that man Will live long as he can! Though miles apart, we'll share the beauty she displays.
from 陆林 编注．宋词．北京：北京师范大学出版社，1992年11月版：第59-60页
嬋 = beautiful, lovely, pretty, graceful, lady-like.
娟 = pretty, good-looking, graceful, attractive.