1. Could you tell me which kind of payment terms you'll choose?

能否告知你们将采用哪种付款方式?

还能这样说：

Could you tell me how you will pay for it?

Could you tell me what your payment terms are?

应用解析：

on easy terms 以分期付款的方式，以优厚的条件

2. This is the normal terms of payment in international business.

这是国际贸易中惯用的付款方式。

还能这样说：

People usually use this kind of payment in international trade.

This payment is often seen in international business.

应用解析：

be normal to 垂直于，成直角;

off normal 越界的，不正常

3. We will pay in installments.

我们将分期付款。

还能这样说：

We will pay on easy terms.

We can buy it on an installment basis.

4. They demand prompt payment.

他们要求立即付款。

还能这样说：

They demand to pay immediately.

They require that we should pay at once.

应用解析：

be prompt to obey commands 立即服从命令;

prompt sb.'s thought 激起某人的思想;

prompt sale 期货交易