Who says "I heard a language that I didn’t know" (81:5), and where do God's words begin?

The psalm doesn't say who says it. The verse reads, "He appointed it in Joseph for a covenant, when he went out over the land of Egypt, I heard a language that I didn’t know" (81:5). In Hebrew I heard and I didn’t know are in the first person, like the I of the next verse, but the WEB leaves 81:5 outside its quotation marks and opens them at 81:6: "I removed his shoulder from the burden" (81:6). The Hebrew has no quotation marks, so the WEB's are a reading of where the words change hands. What the psalm does make plain is who speaks in the verses that follow: "I am the LORD, your God, who brought you up out of the land of Egypt" (81:10). It doesn't say whose I is in 81:5, or what language was heard, and these notes don't either.