Learn Spanish (Latin America): Leímos el nuevo decreto, según el cual hay que pagar. - We read the new decree, according to which we must pay.

In Spanish, when a relative pronoun comes after certain prepositions—especially longer ones like según (according to)—you generally cannot use just que. You must use a compound pronoun like el que or el cual. Because this sentence is talking about a formal legal document (el decreto), the formal pronoun el cual is the most natural fit.

How do I know to use el cual and not la cual or los cuales here?

These formal relative pronouns always have to match the gender and number of the noun they refer back to. Here, "which" refers back to el decreto, which is a masculine, singular noun. Therefore, you must use the masculine, singular form: el cual.

Could I use el que instead of el cual in this sentence?

Yes, según el que is also grammatically correct and means the exact same thing. However, el cual is preferred in formal speech and writing, which makes it perfect for a sentence about reading a government decree!

The translation says "we must pay," but I don't see a conjugated verb for "we". Where does that come from?