I spoke Spanish while doing a voiceover for a vlog. Is it correct to say, “I snapped on the Spanish part”?

Yes, saying “I snapped on the Spanish part” could be understood informally to mean that you performed exceptionally well or felt confident when delivering that portion in Spanish. However, "snapped" is more commonly used in informal contexts to describe a strong emotional reaction or sudden outburst. If you want to express that you did well or excelled in the Spanish part, you might say something like, “I really nailed the Spanish part” or “I crushed it on the Spanish part.”