How is 那还用说！translated as "Of course!" or "That goes without saying!"?

Question

Could anyone please tell me how these characters mean "Of course!"/"That goes without saying!" when placed together?

Because when it's translated one by one, the characters don't seem to correlate to one another at all.

那 : that
还 : still
用 : use
说 : speak

I'm just curious though.

Answer 1

The point is 用 doesn't mean "use", but "need" here.

（多用于否定: 需要） need:

There's no need to turn on the light.
不用开灯。

I don't think you need to worry in the least.
我看你一点也不用着急。

And 还 is used for emphasis,

（用以加强语气）:

That goes without saying.
那还用说!

This is the limit!; This is simply atrocious!
这还了得!

那还用说 is a rhetorical question (echo question), it literally means ”need to say that?!", i.e. "no need to say", then "of course" or "that goes without saying".

Answer 2

那还用说！ means "not even deserves to mention it", implying something is very obvious and no need to address it or put it on the table.

Stretch a bit:

那：that thing

还用（equal to 不用）：not necessary to

说：speak, mention