2 Heb “at the new moon.” New moon festivals were a monthly ritual in Israel (see R. de Vaux, Ancient Israel, 469–70). In this context the New Moon festival of the seventh month, when the Feast of Tabernacles was celebrated (note the reference to a “festival” in the next line), may be in view.
3 Heb “at the full moon on the day of our festival.” The Hebrew word כֶּסֶה (keseh) is an alternate spelling of כֶּסֶא (kese’, “full moon”). The festival in view is probably the Feast of Tabernacles (Booths), which began on the fifteenth day of the seventh month when the moon was full. See Lev 23:34; Num 29:12.
4 Heb “because a statute for Israel [is] it.”
5 Heb “in his going out against the land of Egypt.” This apparently refers to the general time period of Israel’s exodus from Egypt. The reads, “from Egypt,” in which case “Joseph” (see the preceding line) would be the subject of the verb, “when he [Joseph = Israel] left Egypt.”
6 Heb “a lip I did not know, I heard.” Here the term “lip” probably stands for speech or a voice. Apparently the psalmist speaks here and refers to God’s voice, whose speech is recorded in the following verses.

In other versions

ESVEnglish Standard Version

Blow the trumpet at the new moon,

at the full moon, on our feast day.

For it is a statute for Israel,

a rule of the God of Jacob.

He made it a decree in Joseph

when he went out over the land of Egypt.

I hear a language I had not known:

NIVNew International Version (2011)

Sound the ram’s horn at the New Moon,

and when the moon is full, on the day of our festival;

this is a decree for Israel,

an ordinance of the God of Jacob.

When God went out against Egypt,

he established it as a statute for Joseph.

I heard an unknown voice say:

CSBChristian Standard Bible

Blow the trumpet on the day of our feasts

during the new moon

and during the full moon.

For this is a statute for Israel,

an ordinance of the God of Jacob.

He set it up as a decree for Joseph

when he went throughout the land of Egypt.

I heard an unfamiliar language:

NLTNew Living Translation

Blow the ram’s horn at new moon,

and again at full moon to call a festival!

For this is required by the decrees of Israel;

it is a regulation of the God of Jacob.

He made it a law for Israel

when he attacked Egypt to set us free.

I heard an unknown voice say,

LEBThe Lexham English Bible

Blow the horn at new moon,

at full moon, for our feast day,

because it is a statute for Israel,

an ordinance of the God of Jacob.

He made it a statute in Joseph

when he went out against the land of Egypt,

where I heard a language I did not know.

KJV 1900King James Version

Blow up the trumpet in the new moon,

In the time appointed, on our solemn feast day.

For this was a statute for Israel,

And a law of the God of Jacob.

This he ordained in Joseph for a testimony,

When he went out through the land of Egypt:

Where I heard a language that I understood not.

Public Domain