וַיֹּ֣אמֶר יְהוּדָ֗ה מַה־נֹּאמַר֙ לַֽאדֹנִ֔י מַה־נְּדַבֵּ֖ר וּמַה־נִּצְטַדָּ֑ק הָאֱלֹהִ֗ים מָצָא֙ אֶת־עֲוֺ֣ן עֲבָדֶ֔יךָ הִנֶּנּ֤וּ עֲבָדִים֙ לַֽאדֹנִ֔י גַּם־אֲנַ֕חְנוּ גַּ֛ם אֲשֶׁר־נִמְצָ֥א הַגָּבִ֖יעַ בְּיָדֽוֹ׃
Entonces dijo Judá: ¿Qué diremos á mi señor? ¿qué hablaremos? ¿ó con qué nos justificaremos? Dios ha hallado la maldad de tus siervos: he aquí, nosotros somos siervos de mi señor, nosotros, y también aquél en cuyo poder fué hallada la copa.
Rashi on Genesis
האלהים מצא GOD HATH FOUND OUT — We know that we have done no wrong, but it has been brought about by the Holy One, blessed be He, that this should come upon us. The Creditor has found an opportunity to collect His debt (Genesis Rabbah 92:9).
Sforno on Genesis
What shall we say. What can we say in response?
Or HaChaim on Genesis
מה נאמר מה נדבר, "What can we say, how can we speak?" The expression אמירה refers to mild talk, whereas the expression דבור refers to aggressive, tough talk. When the brothers added: מה נצתדק, "how can we justify ourselves?," they referred to their defence in a court of law. They considered that all these trumped up charges were retribution by G'd. The time apparently had come to pay for their guilt. Inasmuch as they were all guilty vis-a-vis G'd, they offered themselves as slaves.