I just peer commented that:

    FWiW if immigrants are not assimilating I'd put that down to what resources are being put into integrated housing, education, etc. and whether those resources are stretched, etc.

which is a crux, given populations can only assimilate so many new people in any given time period and that is mediated by how much effort goes toward welcoming people in.

We have examples in Australia over the past six decades that demonstrate segragated communities with no programmed support remain isolated from mainstream society for longer than communities that are spread about more and given support to find work, learn languages, and have their children make friends with other Australian children.

I don't know enough about Sweden and Germany to comment on the issues they are currently facing.