快乐 isn't really used this way in China. It is mostly ised to wish people a "happy something". 开心 kaixin or 高兴 gaoxing make more sense when talking about the happiness of someone.
Is there a difference between this & 你高兴吗?
I just remember that song from the 90s... Ni kuai le ma? Wo hen kuai le...
Don't worry, be happy.
I think a better translation for this might be "Are you contented?"
I would translate 'contented' or 'content' as 滿意.