en_tn/pro/26/09.md

Like a thorn ... is a proverb in the mouth of fools

How the two are alike can be stated clearly. Alternate translation: "A proverb in the mouth of fools is as dangerous as a thorn that goes into the hand of a drunkard" (See: rc://en/ta/man/translate/figs-simile)

a thorn that goes into the hand of a drunkard

Possible meanings are 1) if a drunk person holds a thornbush, a thorn will prick his hand, or 2) if a drunk person is angry, he will pick up a thornbush and swing it at people. For the second meaning, the word "thorn" represents a thornbush. (See: rc://en/ta/man/translate/figs-synecdoche)

in the mouth of fools

Here "mouth" is a metonym for speaking. Alternate translation: "in the speech of fools" or "that fools say" (See: rc://en/ta/man/translate/figs-metonymy)