Learn French: Je ne suis pas encore confiant, mais l'équipe l'est.

This l' is the neuter pronoun le. In English, we can drop the adjective and just say "the team is." In French, you cannot leave the verb être hanging; you must refer back to the adjective or state being discussed. The le here acts like "it" or "so," meaning "the team is (confident)."

Since l'équipe is a feminine noun, why wouldn't we use the feminine pronoun la?

When you use a pronoun to replace an adjective (in this case, confiant) rather than a specific noun, you always use the invariable neuter pronoun le. It never changes to agree with the subject's gender or number. It just contracts to l' because est starts with a vowel.

How do we know the gender of the speaker (Je) in this sentence?

The adjective confiant is in its masculine form. If the speaker were female, she would say Je ne suis pas encore confiante. Interestingly, even if the speaker were female, the second half of the sentence (l'équipe l'est) would remain exactly the same, because the neuter pronoun le never changes.

Could I say Je ne suis pas confiant encore?

No, it sounds unnatural. The phrase pas encore (not yet) acts as a single negative unit here. The encore must directly follow pas and come before the adjective, rather than floating at the end of the clause.