19 The translation assumes the Niphal is passive; another option is take the clause (note the subject + verb pattern) as concessive and the Niphal as reflexive, “though he humbled himself.”
20 This verse emphasizes the servant’s silent submission. The comparison to a sheep does not necessarily suggest a sacrificial metaphor. Sheep were slaughtered for food as well as for sacrificial rituals, and טֶבַח (tevakh) need not refer to sacrificial slaughter (see Gen 43:16; Prov 7:22; 9:2; Jer 50:27; note also the use of the related verb in Exod 21:37; Deut 28:31; 1 Sam 25:11).

In other versions

He was oppressed, and he was afflicted,

yet he opened not his mouth;

like a lamb that is led to the slaughter,

and like a sheep that before its shearers is silent,

so he opened not his mouth.

He was oppressed and afflicted,

yet he did not open his mouth;

he was led like a lamb to the slaughter,

and as a sheep before its shearers is silent,

so he did not open his mouth.

He was oppressed and afflicted,

yet he did not open his mouth.

Like a lamb led to the slaughter

and like a sheep silent before her shearers,

he did not open his mouth.

He was oppressed and treated harshly,

yet he never said a word.

He was led like a lamb to the slaughter.

And as a sheep is silent before the shearers,

he did not open his mouth.

He was oppressed and afflicted,

yet he did not open his mouth;

he was brought like a lamb to the slaughter,

and like a sheep is dumb before its shearers,

so he did not open his mouth.

He was oppressed, and he was afflicted,

Yet he opened not his mouth:

He is brought as a lamb to the slaughter,

And as a sheep before her shearers is dumb,

So he openeth not his mouth.

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