I dunno about other countries but the concept of America is that you should be able to come here and celebrate your own culture, not just have to conform to ours, that's why they call it a melting pot. As long as their culture doesn't interfere with anyone else's well-being, I don't see why they'd have to assimilate.
If you study patterns of immigration to this country, you will find that until just before 1900, fully 90% of the people who came to the USA were from Europe, and mostly northern Europe at that.
They had different languages and different cultures, and in many cases, different religions, ie., Protestant and Roman Catholic and various subsets of both. That being said, in large measure, the immigrant generation saw to it that their children and grandchildren assimilated.
The so-called melting pot was more of a mixed European melting pot than anything else during the period prior to the turn of the last century.
The same was not true for easily identifiable groups, ie.; Hasidic Jews, whose manner of dress alone, tended to set them apart; Chinese immigrants who were more or less separated by a barrier of color; the Amish; and so on.
Many of the latter groups managed to settle in immigrant communities or enclaves and, for the most part, did not demand special treatment.
Muslim immigrants are a different story altogether. They are demanding to be treated differently in this country just as they are in Europe and the UK. The UK, in particular, has bent over backward to accommodate its Muslim population, but to no avail. They keep wanting more and more.
Many people think it's time to draw a line and say - if you want to be a citizen, learn the language and have some respect for our culture.
Borders, Language, and Culture are what define a country.
