I'm glad for you, but that quote is a huge simplification of a nuanced theme. Maybe it's hard for a completely different ethnicity to become parisienne, but I'm sure France is a big country. Maybe it applies to Japan, but not to Spain. Etc.

I have been to America and it feels lots of different countries living in the same place, not necessarily a good thing. Again it's a subject full of nuances, but I have seen different people being completely integrated after just a single generation. What I think is relevant is how much a culture is exposed and capable of absorb different people from different cultures.