"Yo hablé mucho en español."
Translation:I spoke a lot in Spanish.
Most of the time, you don't need the personal pronouns. In fact when you add them, it emphasizes that pronoun and gives a slightly different meaning. Hablé español. I spoke Spanish. Yo hablé español. (Look at me. I showed off my skills and) "I" spoke Spanish. Or I spoke Spanish (but others didn't) for examples. It would depend on context.