何とも言い難いな。の英語

That's hard to say.

I cannot say.

I can't say.

I can't say for sure.

I don't know what to say.

I'm at a loss for words.

I just don't know what to say.

I am not certain [sure].

I can't say for certain.

I can't say anything.

There is no way of expressing it―It is unspeakable―unutterable.

（文頭に置けば）―There is no saying―（文尾に置けば）―for aught one knows―（独立句に用いれば）―Who knows?―God knows―（形容詞に用いれば）―unspeakable sorrow―inexpressible feeling―indescribable beauty―unutterable grief―ineffable joy―indefinable charm―exquisite pleasure

Who knows?

God knows.

You know what it is.

It goes without saying.

It's not worth mentioning.

Can't say anything

Some things are better left unsaid.

It is not worth mentioning specially.

I'm not saying anything.

There is no saying what may happen.

What can I say about it?

I have nothing to say about it.

I do not know what excuse to make.

I could not speak from fear.

I told you so!

I need scarcely say.

I can't tell.

I don't know what excuse to make