なんとも言えない形をしているの英語

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

I don't know what excuse to make

I don't know what to say.

I am not certain [sure].

Can't say anything

I am dumfounded―I am struck dumb with astonishment―astonishment deprives me of my power of speech.

There is no saying what may happen.

You need not speak so tediously―go into such details.

I do not know what excuse to make.

I'm not saying anything.

You can have nothing to complain of―nothing to grumble at.

I cannot say.

to cease to speak

No comment!

Stop being unreasonable.

That's hard to say.

I can't say for sure.

There is no saying what may happen.

having an aspect of not saying anything concretely

of a person, to become totally uncommunicative

I need scarcely say.

to be unable to speak

What can I say about it?

The statement is too sweeping.

The statement is too sweeping.

the feeling of being impatient

the state of being impossible to fully express in words

He weighs every word he utters

It is not worth mentioning specially.