כִּ֛י י֥וֹם נָקָ֖ם בְּלִבִּ֑י וּשְׁנַ֥ת גְּאוּלַ֖י בָּֽאָה׃
װאָרום אַ טאָג פֿון נקמה איז אין מײַן האַרצן, און מײַן יאָר פֿון דערלײזונג איז געקומען.
Ibn Ezra
For the day of vengeance, etc. For I will wreak vengeance against my enemies, and I will redeem my friends. גאולי My redeemed. It is participle passive plural with the suffix, first person, referring to God.
Tze'enah Ure'enah
“For I had planned a day of vengeance and My year of redemption arrived” [63:4]. I have had a day in My heart on which to take vengeance and the year of redemption has come.