It's a chance for all the different nationalities .......................................... live in Dublin to share their culture.
Hi, Treasure—I think Gustavo has made a good argument for choosing "who" in this particular sentence. As usual, I don't feel obligated to confine myself to a fill-in-the-blank task, rejoicing in my freedom to revise a sentence at will.
(1) It's a chancefor people of all the different nationalities in Dublin to share their culture.
(2) It's a chance for all the different nationalities of Dubliners to be shared.
I'd say that saying a person of a certain nationality lives somewhere is different from saying that the nationality itself lives there. And, yes, I am aware someone could object that some definitions identify nationality with a group of people. Personally, I'd say that nationalities are not sentient except when personified.