Question

The next important question we have to decide is when do we have to submit the proposal.

为什么这么改
do we have to-----we have to

Answer 1

The next important question we have to decide is
我们需要决定的下一个问题是
（意译： 重要的下一步，是决定 ... ）

when do we have to submit the proposal
何时必须提交投标（或提案）

放在一起：
The next important question we have to decide is when do we have to submit the proposal.
重要的下一步，是决定何时必须提交投标（或提案）

希望帮到了你，满意敬请采纳，谢谢。