Learn Italian: Le lenzuola sono sporche, le devi lavare. - The sheets are dirty, you must wash them.

This is one of those tricky irregular plurals! The singular word for "sheet" is il lenzuolo, which is masculine. But in the plural, it changes its ending to -a and becomes a feminine plural noun, le lenzuola.

Why is the adjective sporche instead of sporchi?

Because the irregular plural le lenzuola acts as a feminine noun, any adjectives describing it must also be feminine plural. The word for "dirty" is sporco. Its feminine plural form is sporche (an "h" is added to keep the hard "c" sound).

In le devi lavare, what does le mean here?

Here, le is a direct object pronoun meaning "them", referring back to the feminine plural le lenzuola. It is placed right before the conjugated verb devi.

Could I say devi lavarle instead of le devi lavare?

Yes! When you have a conjugated verb followed by an infinitive (like devi lavare), you can either put the pronoun before the first verb (le devi lavare) or attach it to the end of the infinitive by dropping its final -e (devi lavarle). Both are perfectly correct.