這是典型的中國文化的詞彙表達。外華人不一定知道“東海”和“南山”，但是一定知道“海”有多深，“山”有多高。有如大海那麼寬廣無邊的“福”，有高山那麼高的“壽”，當然是三生有幸的美事了。所以，這兩句漢語可以直譯，如：

May your age be as the southern mountain and your happiness as the eastern seas.

May your happiness be as boundless as the eastern seas and your life as long as the long lasting southern mountains.

然而，在一定的情況下，不一定那麼譯。如：

I wish you boundless happiness and a long, long life.

Much happiness and a long, long life to you.

其實，在祝賀某人的生日時，英語表示“福壽無邊，長命百歲！”的表達法，也有如上漢語表達的神韻：

Many happy returns (of the day)! 福壽無邊，長命百歲！

方法是多樣的，不會一成不變。看場合，看語境，靈活運用，才得神韻。

最後再提供兩個翻譯的版本：

1.Bless

the old that their happiness be like the East Sea,and longevity over the southern hill.

2.May

your fortune be as boundless as the East Sea and you live a long and happy life.