How do you say hip hooray in welsh?

There isn't a direct equivalent of "hip hooray" in Welsh. The closest you could get would be to use the phrase:

"Hwyl fawr!"

This translates to "Have a good time!" or "Cheers!" It's a common way to express excitement and enthusiasm, similar to the spirit of "hip hooray."

You could also try:

"Hurrah!"

This is an English word, but it's often used in Welsh as well.

Ultimately, how you express excitement depends on the specific context.