Question: Do you believe it's an immigrant's obligation to assimilate?
Answer: Yes and no. If one is immigrating to a basically decent country, then yes, one has an obligation to abide by the basic principles that make that decent country a decent country. Beyond that though, no. A basic principle of decent countries is liberty; the right to adopt all sorts of particular lifestyle choices, whatever they are; to speak whatever language you want, dress how you want with respect to religion, music and hundreds of other things.
One had no obligation in a decent, free country to assimilate to the particular lifestyle choices of other people, even a majority of people in that country. One has only an obligation to assimilate, rather to say, the principles of individual rights and to live by those.