Formal:
* Je devrai: This is the most literal translation and is used in formal situations.
* Je dois: This is another formal option, but it implies a stronger sense of obligation.
Informal:
* Je vais: This is the most common way to say "I shall" in informal situations. It simply means "I am going to."
* Je vais devoir: This is a more informal way to say "I shall have to."
Here are some examples:
* Formal: Je devrai travailler tard ce soir. (I shall work late tonight.)
* Formal: Je dois aller à la réunion. (I must go to the meeting.)
* Informal: Je vais manger une glace. (I am going to eat an ice cream.)
* Informal: Je vais devoir me coucher tôt. (I am going to have to go to bed early.)
It's important to choose the correct translation based on the context and your relationship with the person you are speaking to.