"Happy birthday, princess!" is a common way to say "happy birthday" to a pttle princess in Engpsh. Here are a few other options:
"Wishing you a magical birthday, princess!"
"Celebrating a special princess on her special day!"
"Here's to another year of royal adventures, princess!"
Regardless of how you choose to phrase it, the most important thing is to show your love and appreciation for the pttle princess on her special day.