How do you say so long be seeing in french?

There isn't a direct translation of "so long, be seeing you" in French. However, here are some ways to say goodbye with a similar meaning:

Informal:

* À plus tard! (See you later!)

* À tout à l'heure! (See you soon!)

* Ciao! (This is Italian, but commonly used in French)

* On se voit! (See you!)

* Bonne journée! (Have a good day!)

* Bonne soirée! (Have a good evening!)

More formal:

* Au revoir! (Goodbye)

* Bonne journée/soirée! (Have a good day/evening)

* À bientôt! (See you soon!)

You can also use a combination of phrases, such as: "À plus tard, et on se voit!" (See you later, and I'll see you!)

The best way to choose a goodbye phrase depends on the context and your relationship with the person you are saying goodbye to.