I'll say it's simpler than that: make sure immigrants get to sustain themselves through work rather than welfare. This creates a direct incentive for them to learn the language and actually integrate into the new society.
The great problem Europe has with migrants is not the inherent "poor imported stock", but the lean welfare rules and strict employment rules. This ensures a toxic proportion of new arrivals simply don't want to or can't integrate. It also means you get second-generation immigrants with no better prospects than their parents.