Here are some possibilities, along with their nuances:
1. "deber" - (to have to, ought to)
* This is the most common translation when "shall" expresses obligation or duty.
* Example: "We shall pay our debts" -> "Debemos pagar nuestras deudas."
2. "tener que" - (to have to)
* Similar to "deber," but can sometimes be used in a less formal context.
* Example: "I shall go to the store" -> "Tengo que ir a la tienda."
3. "ir a" + infinitive - (to be going to, will)
* Used to express future intention, similar to "will."
* Example: "I shall return tomorrow" -> "Voy a regresar mañana."
4. "haber de" - (to be due to, must)
* Less common, but can be used to express a future obligation or strong intention.
* Example: "He shall be punished" -> "Ha de ser castigado."
5. "va a" + infinitive - (is going to, will)
* Similar to "ir a," but can also express a future certainty.
* Example: "The sun shall rise tomorrow" -> "El sol va a salir mañana."
6. "será" - (will be)
* Used to express a future prediction or certainty.
* Example: "The day shall come when..." -> "Llegará el día cuando..."
7. "tendrá que" - (will have to)
* A more formal way of expressing a future obligation.
* Example: "You shall have to explain yourself" -> "Tendrás que explicarte."
The best translation of "shall" will depend on the specific context and nuance of the sentence. Consider the intended meaning and the formality of the situation when choosing the appropriate Spanish equivalent.