I'm curious. While the lessons present a number of ways to wish someone a happy birthday, "frohe Geburtstag" is not among them. That was what we were taught decades ago in my high school & college German classes. Is that outdated? Regional? Only something you see in writing, not spoken? Overly formal? Slang?
June 16, 2021
June 21, 2021
Guten Tag RobertD50!
The most common phrases for wishing someone a happy birthday are “Alles Gute zum Geburtstag!" and “Herzlichen Glückwunsch (zum Geburtstag)!” You could say “Frohes Geburtstagsfest!” - “Happy birthday party!”, however this would be less common.
For festive occasions such as easter and christmas it is more common to use “frohe” as in “Frohe Ostern!” - “Happy Easter!" and “Frohe Weihnachten!”- “Merry Christmas!"
Hope this helps!