难以启齿的英文：
unspeakable
difficult to speak one’s mind

参考例句：

You probably have a few skeletons in your own closet.
你说不定也有一些难以启齿的秘密吧。

It was fatso who first spoke of the unspeakable thing
这件难以启齿的事还是让胖嫂先说穿了。

I was so overpowered by my guilt and my shame that I was unable to speak.
内疚和羞愧令我无地自容，难以启齿。

Computer programs aid parents who want their kids to have the facts of life but who are uncomfortable discussing them.
希望子女了解性知识，而又觉得难以启齿的父母，可以通过电脑软件来讲解。

unspeakable是什么意思：
a. 无法形容的

An unspeakably vile habit.
不可言状的坏习惯。

Unspeakable cruelty, behaviour,embarrassment
难以形容的残忍、行为、尴尬

Unspeakable joy,delight,etc
说不出的快乐、喜悦等.

difficult是什么意思：
adj. 困难的；执拗的；不易相处的

The exercise is that difficult!
练习题那么难！

You must admit the task to be difficult [ that the task is difficult ].
你应当承认这项任务是艰巨的。

You must admit the task to be difficult [that the task is difficult].
你必须承认这项任务是困难的。

speak是什么意思：
v. 谈话；说话；提起；会讲；…行话；演讲；代表；表明；显示；不言而喻

Don't speak for your friend, speak for yourself.
不要代表你的朋友发言了，谈谈你自己的看法吧。

Don't speak for your friend,speak for yourself.
不要代表你的朋友发言了，谈谈你自己的看法吧。

It is one thing to speak much and another to speak pertinently
话讲得多是一回事,讲得恰当是另一回事