Let's break it down:
* Le: This is the informal "he/she" in Spanish.
* gusta: This is the third-person singular form of the verb "gustar" which means "to like."
* cuando: This means "when."
* hablo: This is the first-person singular form of the verb "hablar," which means "to speak."
* en español: This means "in Spanish."
Putting it all together, the sentence conveys that someone enjoys hearing the speaker speak Spanish.