Actually good question.

I'd say probably not. You can't easily "unlearn" things from the model weights (and even if this alone doesn't help). You could retrain/finetune the model heavily on a single language but again that alone does not speed up inference.

To gain speed you'd have to bring the parameter count down and train the model from scratch with a single language only. That might work but it's also quite probable that it introduces other issues in the synthesis. In a perfect world the model would only use all that "free parameters" not used now for other languages for a better synthesis of that single trained language. Might be true to a certain degree, but it's not exactly how ai parameter scaling works.