• Your birthday is a very joyful day, a day you can never forget. It is common in English to greet people "happy birthday" the day they are celebrating their birthday. Either British English, American English or any other, you say happy birthday.
• But when it comes to French, the most common or the most standard way of greeting happy birthday in French is "Bon Anniversaire," which simply means happy birthday.
• But sometimes, some other French people do say "Joyeux Anniversaire", which majorly means happy celebration or happy anniversary.
• However, some French-speaking parts of Canada also use "bonne fête" to mean happy birthday. So, whenever you want to say happy birthday to your friend or someone else on French, assuming his name is John, just say "Bon Anniversaire John."
Another ways you can go, considering the examples I've made earlier, are "Joyeux Anniversaire John" or "bonne fête John." And he could reply "merci," which simply means "thank you."