In his delight he lifted up his voice and brayed, but then every one knew him, and his owner came up and gave him a sound cudgelling for the fright he had caused. And shortly afterwards a Fox came up to him and said: 「Ah, I knew you by your voice.」 Fine clothes may disguise, but silly words will disclose a fool.
In his delight 在他高興之中
he lifted up his voice 他提高了嗓門，
and brayed, 叫了起來，
but then 但那個時候，
every one knew him, 大家都認出他來了，
everyone只能表示「人」，相當於everybody；但是分開寫成every one，就是「每一個個體」，可以指人，也可以指物。
and his owner came up 然後他的主人走了上來
come up 就是「走上來、走過來」
and gave him a sound cudgelling重重地用棍子打了他一頓
* give sb. sth. 給某人某物，這裡的sth.也就是a sound cudgelling，（一頓重重的棍棒）
sound這個詞，除了可以作名詞表示「聲音」，或者作動詞表示「聽起來」之外，sound也可以作形容詞，表示「完整的」。
He had a sound sleep.（他這一覺睡得很香。）指的是中途沒有醒，從頭到尾的睡眠很完整。
這個故事裡sound理解成「重重的」，突出的就是主人打驢沒有任何手下留情的地方，結結實實打了一頓，所以a sound cudgelling是一個看字面都覺得很疼的表達。
為什麼這麼狠地揍自己的驢呢？後面是for引導的一個原因狀語：
for the fright因為那種恐懼
什麼恐懼呢？然後是後置定語：
he had caused.他造成的（恐懼）。
and his owner came up and gave him a sound cudgelling for the fright he had caused.
翻譯成接地氣的漢語：因為給大家造成了驚嚇，驢主人走過來用木棒將驢暴打了一頓。
And shortly afterwards沒過多久
a Fox came up to him一隻狐狸朝他走來
come up to sb.就是「朝某人走來」
and said:然後說：
「Ah, I knew you by your voice.」「一聽你的聲音，我就知道是你。」
know sb. by sth.也就是「通過某物知道某人」。
最後一句話總結，這個故事蘊含的道理：
Fine clothes may disguise, but silly words will disclose a fool. 漂亮的衣服可以掩蓋傻瓜，但蠢話會將他暴露。
這句話寫得很對稱，前後分別是一個主謂賓的結構，主語是Fine clothes（漂亮衣服）和silly words（愚蠢的話），謂語是disguise（掩飾）和disclose（揭露），賓語都是a fool（一個傻瓜）。