As someone who remembers being on a bus or train, in a shop, a doctor's waiting room or just a park and hearing only English being spoken the different languages I hear now can be disconcerting. Sometimes communication is difficult.
On the other hand my grandchildren are used to mixing with people from many different backgrounds and think nothing of it.
The first situation fostered racism and zenophobia and encouraged nationalism and patriotism. The second situation discourages all of the above. Younger people are much more tolerant and informed about those from other countries and cultures.
The question is whether national identity necessarily involves the population being homogeneous. Some countries have managed it, but is that because all of their populace are relatively recent immigrants?
You raise some interesting and thoughtful points. And I can understand that it may be confusing, but we are all just people. I was fortunate to have brought up with several languages, and work internationally so I see the mix of languages spoken, especially in London, fascinating.
And I feel British first and European second. There is no doubt that we are a sovereign nation, under the British constitution and governed by the British Parliament and laws. In those areas where EU law has overridden English law it is only with the consent of parliament. Our relationship with the EU is as one of the three senior members of the EU.
As a county we have always had immigration - Angles, Saxons, Romans, Normans, Africans, Chinese, Jews, Arabs, Indians, Italians etc etc. It's a big melting pot. And Immigrants who stay have become British.
You are right that the young are more relaxed about differences, and are more global in outlook, and more likely to vote remain, while the old are more likely to vote leave. The young are the future so maybe the older generation should consider their wishes and their future.