Some insights on the language of cats.

The feline language does not have a word for happiness. The closest translations mean something more like contentment, or in on case, satiation.
While there are a few words that translate into things like exuberance or playfullness, these are more descriptors of behavior than emotion.
The reason for this lack of concept is probably due to the fact that cats do not view happiness as an abstract absolute condition, but rather as a condition of being comfortable.
They tend to feel that humans could be saved a lot of trouble if they spent less time trying to find happiness, and more time learning to be content with what they have.