You may ask, " would you please speak more slowly" ?

" 请你说慢一点好吗？"

At the beginning of the conversation, you can ask, " Would you please speak more slowly" ?

在谈话开始时，你可以问：" 请说慢点好吗？"

They've been told for years, " Could you please speak more slowly because I can't understand your accent"

请问你能讲慢一点吗？因为我听不懂你的腔调。

Excuse me. Would you please speak more slowly?

抱歉，可否请您讲慢一点呢？

Would you please speak more slowly?

可否请您讲慢一点呢？

So, it's perfectly okay if you say politely, " Could you please speak more slowly? " Maybe the problem is the person who's speaking is talking way too fast.

所以，如果你礼貌地说：“你能说得慢一点吗”，那就太好了。也许问题在于那个人说得太快了。

And if you're having a lot of trouble, ask a teacher: " Can you please speak more slowly? " And the teacher will slow down, and it will be much easier for you to understand.

如果你有很多困难，问老师：“你能说慢点吗？ ” 老师会放慢语速， 这样你就更容易理解了。