在英语中，“说话不敢大声”可以用不同的词组来表达，常用的有：

Speak softly/quietly/in a low voice：轻声地说话
例句：
He always speaks softly, so it's hard to hear him. 他总是轻声说话，所以很难听到。
Please speak quietly. 请轻声说话。
Be timid/shy/afraid to speak up/out：害羞，不敢说话
例句：
She is so timid that she never speaks up in class. 她太害羞了，从不在课堂上发言。
He was afraid to speak out in front of so many people. 他在这么多人面前不敢说话。
Be hesitant to speak：犹豫不决地说话
例句：
She was hesitant to speak at first, but eventually she gathered the courage to share her opinion. 她一开始有点犹豫不决，但最终鼓起勇气分享了她的看法。
He was hesitant to speak his mind, but I encouraged him to be honest. 他有点犹豫不决，但我鼓励他坦诚相见。

这些词组的意思都与“说话不敢大声”有关，你可以根据自己的需要选择使用。