the only reasons that people have for not learning the language of the country they live in are stupidity and laziness,
Indeed. This does happen, and of course there are Poles in the UK (for a decade or more, not just for the duration of a degree or a training programme) who can't ring for a taxi. Not everyone has the same aptitude for language learning.
ethno-racial and religious mix
Not a consideration.
Good that the increasing number of studenty jobs in Poland is attracting young people who want to study and perhaps settle.