Psalm 68:26, "“Bless God in the congregations, even the Lord in the assembly of Israel!”" is a call to praise and worship God publicly. Let's break down the meaning:

"Bless God": This means to praise, adore, give thanks, and speak well of God. It's an active expression of gratitude and reverence.
"in the congregations": This emphasizes that the praise should be done collectively, as a group of believers gathered together. It's not just a private, individual act, but a communal one.
"even the Lord": This reinforces who they are to bless - Yahweh, the covenant God of Israel.
"in the assembly of Israel!": This phrase emphasizes the specific people who are called to this public worship: the community of Israel, God's chosen people. The "assembly" refers to a formal or organized gathering of the people for religious purposes.

In essence, the verse is a command and an encouragement to the people of Israel to publicly and corporately praise God in their gatherings. It highlights the importance of communal worship and acknowledging God's goodness and sovereignty as a unified body.

Possible interpretations and nuances:

Emphasis on corporate worship: The verse highlights the value of praising God together with other believers. This fosters a sense of unity, shared faith, and collective strength.
Public declaration of faith: Publicly blessing God serves as a witness to others and declares the community's allegiance and devotion to God.
Acknowledgment of God's presence: When the congregation comes together to bless God, they are acknowledging His presence in their midst.
Historical context: Within the context of Psalm 68, which celebrates God's power and victory, this verse is a fitting response of gratitude and praise from the redeemed people.

Today, this verse can be seen as a call to all believers to actively participate in corporate worship and to publicly express their love and gratitude to God within the church or faith community.