en_tn/rom/03/19.md

whatever the law says, it speaks to

Paul speaks of the law here as if it were alive and had its own voice. AT: "everything that the law says people should do is for" or "all the commands that Moses wrote in the law are for" (See: rc://en/ta/man/translate/figs-personification)

the ones who are under the law

"those who must obey the law"

in order that every mouth may be shut

Here "mouth" is a synecdoche that means the words people speak. You can translate this in an active form. AT: "so that no people will be able to say anything valid to defend themselves" (See: rc://en/ta/man/translate/figs-synecdoche and rc://en/ta/man/translate/figs-activepassive)

the whole world held accountable to God

Here "world" is a synecdoche that represents all the people who live in the world. AT: "that God can declare everyone in the world guilty!" (See: rc://en/ta/man/translate/figs-synecdoche)

flesh

Here "flesh" refers to all human beings.

For

Possible meanings are 1) "Therefore" or 2) "This is because"

through the law comes the knowledge of sin

"when someone knows God's law, he realizes that he has sinned"