two chairs facing each other by a window

Asking someone to slow down is a skill, not a confession.

There is a way to ask that keeps the conversation warm, and it works on almost everyone.

Most people ask badly, and then conclude that asking does not work. They say sorry, my English is not good, which does two unhelpful things. It tells the other person the problem is you, and it gives them nothing to act on. They usually respond by getting louder, which does not help at all, or by simplifying so far that the conversation loses its adult shape. You wanted a smaller change than that.

Ask for the specific thing instead. Could you slow down a little, I want to get this right. Sorry, could you say that part again. Do you mind repeating the last bit, I missed the street name. Notice that these name what you need and imply that the rest was fine. They are also warm. Adding that you want to get it right turns the request into care about the task, and people respond to that very well. Nobody objects to being asked to slow down by someone who is clearly paying attention.

It helps to hear the truth about how common this is. Fluent speakers interrupt each other for repeats constantly. Sorry, what. Say again. Which one, the blue one. It is so ordinary that it does not register as an event. When you ask, you are not stepping outside normal conversation. You are joining it.