Yah this phenomenon is called Choral reading/speaking/singing. It works because it re-synchronizes the brain’s speech timing networks through external rhythm, which can be another voice, or even by using a metronome to speak along to at a constant beat per minute, because it’s giving you an external timing source rather that your brain’s internal timing mechanism. Try reading or speaking to a metronome beat, at say 80 bpm, and you’ll find you’ll be fluent. You can download a metronome app on your phone and use that to create the BPM. It’s meant to be a great way to rewire your brains speech motor networks from daily practice.