Barcelona have their reasons for going for Nico Williams instead of Ademola Lookman I don't think it has anything to do with the country of origin of the players, you already know the reason why Barcelona is bringing in Williams to pair with Yamal having watched them play for their country I think the management of Barcelona saw that it will be a good combination playing both players since they are both young and very fast with the ball.
The duet of Nico Williams and Lamine Yamal has proven to bring trophies, we have seen it proven when they played for the Spanish National Team. Barcelona certainly craves that combination, they want to have a sharp and luxurious front line like Real Madrid. The recruitment of Nico Williams will make Hansi Flick job easier, but Barcelona is faced with a difficult situation to complete the deal, the management and club officials must find a way to balance spending so as not to violate FFP rules.