Multiculturalism sprung up from nationalism, as it’s opposite. There is nothing wrong with the concept, but it is too often misused and abused in practice.
In practice the culture of “Other” is often taken as an excuse for our indifference and our inverted chauvinism.
The “Other” is no better in this respect either: he often uses his “culture” as an excuse to perpetuate rigidness, unwillingness to change and accept different standards.