Learn Italian: Quante lingue sai? - How many languages do you know?

The infinitive is sapere (to know). It is a highly irregular verb! While regular verbs ending in -ere follow a predictable pattern, the "you" form of sapere changes its stem completely to become sai.

Wait, I thought "to know" was conoscere. Why use sapere here?

Italian has two different verbs for "to know". Conoscere is used for being familiar with a person, place, or thing. Sapere is used for knowing facts or knowing how to do something. When talking about languages, Italians often use sapere because it implies knowing how to speak them.

Why is the first word quante instead of quanti?

The word for "how many" changes to match the gender and number of the noun it describes. Because lingue (languages) is feminine plural, you must use the feminine plural form quante. If you were asking about masculine plural objects like libri (books), you would use quanti.

Where is the word for "you" in this sentence?