If you’d like to say, Happy Birthday to someobody in French you simply say, “Joyeux Anniversaire“. This literally means, “joyous birthday”. Please note that it’s important to make the liaison between the “x” at the end of “joyeux” and “a” at the beginning of “anniversaire”. By making this link or liaison that “x” will be pronounced as a slight “z” sound.
In this video you can listed to Happy Birthday being sung in French by jibcraip on YouTube. He’s a much better singer than myself so I’ll gladly let you listen to him!
To sing Happy Birthday you simply use the same tune as in English. You sing “Joyeux Anniversaire” three times then on the fourth time you insert the person’s name. Then, sing “Joyeux Anniversaire” one more time.
There are actually a few other ways to say Happy Birthday in French. It is also very common to say, “Bon Anniversaire”. In this situation you need to pronounce the “n” in “bon” because you must link it with Anniversaire as that word starts with a vowel. Also, in Québec (French speaking Canada) you can say, “Bonne Fête” for Happy Birthday. Bonne means good and “Fête” can mean party, festival or holiday.