1) Speak more slowly, please.

请说慢一点。
2) Please speak more slowly.

请说慢一点儿。
3) A little more slowly, please.

请讲慢一点。
4) Could you please speak slowly?

请你说慢点好吗?
5) Serve it a little slower, please.

请把球发慢一点。
6) Speak softer, please.

请说得轻一点。
参考词条