I just drop in to say that "nationalism" is different thing from "racism", but okay.
Even though the question was directed at NA players, I in my special bubble answer: On EUNE I don't really pay much attention on things like nationality (or race - how could I tell race anyways?) other than that either people use english or they don't. If they don't, I don't usually attempt to communicate with them more than "Please use english if you wish to tell me something." Thus race/nationality have pretty much nothing to do with us trying to murder each other on the Murder Bridge from my point of view.
I haven't really detected any racism/nationalism problems. Well, it might have to do with me refusing to listen to all-chat and focusing on the match so hard that I often miss what people are talking in team chat too. I am too simple minded to focus on two things at once, sorry. :)