en_tn/isa/09/07.md

Of the increase of his government and of peace there will be no end

"As time passes he will rule over more and more people and enable them to live more and more peacefully"

rules on the throne of David

Sitting on the "throne of David" is a metonym for having the right to rule; only David's descendants could be king over Israel. Alternate translation: "has the right to rule as David's descendant" (See: rc://en/ta/man/translate/figs-metonymy)

his kingdom, to establish it and sustain it with justice and with righteousness

This can be translated as a new sentence. Alternate translation: "his kingdom. He will establish and protect his kingdom, and he will do what is fair and just"

Yahweh of hosts

See how you translated this in Isaiah 1:9.