This is rather a philosophical rather than linguistic question. The best answer to it is probably to read Aristotle's book called 'The Nicomachean Ethics' (you will certainly be able to find a translation in Chinese).
My own short answer would be something like 'happiness is finding something to value in your life that is more important to you than yourself, and then using all your power and resources to nurture it and make it grow.'
That 'something' could be your children, your family, your career, your dream, your lover, friends or a combination of all these things. One thing it would NOT be for me would be money, except insofar as I need money to help promote the well-being of those I love.