The first time this expression was used was in Genesis 22:17.
I will surely bless you, and I will surely multiply your offspring as
the stars of heaven and as the sand that is on the seashore. And your
offspring shall possess the gate of his enemies
The significance of gate of a city is the place where administrative and judicial gatherings happen, hence some translations' use of "cities". The gate of a city represented the point of power as it regulates access to the city. It controls what goes into the city and what comes out of it.
What does it mean to take possession of the gate of the enemy? Taking possession of the gate of the enemy implies exercising control over that city. It implies taking over a colony. It implies having a city, a colony or an empire yielding to the control of a colonizing external force.
The gates to a city, then, represented a point of power, a place to
exercise control over that city. A military conqueror would try to get
control of the gate in order to enter the city most easily. A king who
had the hearts of the elders who sat in the gate would politically
control the city. A person who organized and ran the commercial market
and storehouses at the gate would control the economic life of the
city—and its surrounding villages. At the gate ideas and policies
flowed along with the commerce. These ideas could result in the rising
or falling of rulers and even nations. And that brings us to the
modern day in which we live. In our lives—in our cities, states,
nations—it often seems like an enemy of the Kingdom of God has
possessed our “gates.” This enemy represents ideals and principals
contrary to that of Heaven’s Kingdom. Yet it influences our business
life, our cultural life, our social life, our political life—even our
church life.
Source: https://sidroth.org/articles/possessing-gates/
Is it attested in other languages or cultures in the region? This has a deep spiritual essence in the languages or cultures in the religion of the city in question. When an external force assumes control over the city of the enemy they stand a great chance of determining the languages and what the religious culture of the target city will look like. It is worthy of not here to state that the enemies being conquered would simply have no form of influence as to what happens to them afterwards. As Paul puts it in his letter to the Romans.
Do you not know that if you present yourselves to anyone as obedient
slaves,[c] you are slaves of the one whom you obey . . . (Romans 6:16
ESV)
Does it presume conflict and victory or has it generalized to simply "be successful"? No! The process cannot be generalized to simply “be successful” because the conquering forces must expect some degree of resistance from the enemies they expect to conquer. Taking the gate of the enemies may begin with conflict. But one thing is certain -- the conflict can only end in the defeat of the enemies.
