לַנָּכְרִ֣י תַשִּׁ֔יךְ וּלְאָחִ֖יךָ לֹ֣א תַשִּׁ֑יךְ לְמַ֨עַן יְבָרֶכְךָ֜ יְהוָ֣ה אֱלֹהֶ֗יךָ בְּכֹל֙ מִשְׁלַ֣ח יָדֶ֔ךָ עַל־הָאָ֕רֶץ אֲשֶׁר־אַתָּ֥ה בָא־שָׁ֖מָּה לְרִשְׁתָּֽהּ׃ (ס)
타국인에게 네가 꾸이면 이식을 취하여도 가하거니와 너의 형제에게 꾸이거든 이식을 취하지 말라 그리하면 네 하나님 여호와께서 네가 들어가서 얻을 땅에서 네 손으로 하는 범사에 복을 내리시리라
Rashi
לנכרי תשיך UNTO AN ALIEN THOU MAYEST LEND UPON INTEREST (according to Rashi: TO AN ALIEN THOU MAYEST PAY INTEREST) — but not to thy brother. Such a prohibition which is not plainly stated but can only be drawn by inference from a positive command is itself regarded only as a positive command — so that one who pays interest to his brother transgresses two negative commands: לא תשיך in v. 20, ולאחיך לא תשיך in v. 21 and a positive command לנכרי תשיך — ולאחיך לא (cf. Sifrei Devarim 263:1; Bava Metzia 70b; also cf. Rashi on Deuteronomy 14:20).
Chizkuni
לנכרי תשיך, “you may charge interest to gentiles.” (According to some authorities this is even a positive commandment. Maimonides and Sefer Hachinuch). All other nations are called gentiles when compared to the Israelites. Compare Ovadiah 11: ונכרים באו שעריו גם אתה כאחד מהם, “the gentile nations came to its gates, you were as one of them.” Compare also Judges: 19,12, and Solomon’s prayer in Kings I 8,41.
Sforno
לנכרי תשיך, you are allowed to pay interest to the gentile (on your loan from him) and you must not betray his trust by citing the prohibition to charge or collect interest.