Spirictum, start a game and look through the Servopedia (I keep forgetting how to spell that), specifically at Nations, Leaders, and Traits. [F12]
The only thing that the Nation chosen will give you is the base culture (IE: European, South American, etc) and determine the appearance of your units and cities. Well, it will also limit the Leader(s) you can choose from, so it may be best to just look at those.
The Leader that you select will determine which two Traits you have. This is important. Well, it can be. That depends on a person's playstyle, and since you said that yours changes a lot, perhaps it is not important to you.
As a note, any player who does not care who their Leader is can have their own selection set to Random. This is a player-by-player setting and thus does not have to be everyone or nobody.
Do remember, you are not choosing a Culture. Those have to be built as Wonders during play. You are choosing a base culture (which does limit which full Cultures you can access), and two Traits.
As a thought related to choosing, would we want to limit each base culture to one player? This would be to have a wider overall selection of Cultures built during the game, and mean less competition for them for each player. Admittedly, this point would have been better to make before anyone had selected a Leader, but I had not thought of it then. If so, the "Pirate Empire" is considered European. Of course, if we do this, then everyone will have to choose, as a Random leader might overlap.