6 million immigrants sounds about right - we have a pensions timebomb in many countries, including Poland
Clearly you don't understand anything about economics regardless of the language it is published in. And if you actually worked yourself you might also understand first hand about how the labor market works.
Here's a little insight for you: people will do any job they are qualified or capable of doing if the pay and other compensation makes it worth their time and effort. Importing labor is an admission that employers do not want to pay the going rate (i.e., at the very least a livable wage) and the locals know it and that is why they turn it down. And like with immigrants in other Western countries the Ukrainians and other migrants "doing the work in Poland that Poles don't want to do" today won't want to be doing it in the future either. Their offspring certainly won't. Migrants don't want to spend their entire working years doing menial work for wages that won't get them and their families ahead in life. But that's commonsense and explains why this reality sails high over your head.
Your "pensions time bomb" excuse is laughable as well.
First off, why should anyone have any concern about the standard of living for self-important, self-regarding Baby Boomers as they enter retirement? They don't have a reputation for ever ensuring their parents lived comfortably and with dignity in their retirement years. And it was the Baby Boomer generation which didn't have enough offspring to ensure replacement level of the population. They were too busy with one-upmanship with their neighbors. Most frittered away their money and in practically every Western country voted in successive governments which racked up debt through borrowing. Sorry, but ef' them dear.
Secondly, governments across the EU are spending BILLIONS upon BILLIONS upon BILLIONS on migrants:
Germany Puts Migration-Related Costs at Over $86 Billion Over Next Four YearsSource: wsj.com/articles/germany-puts-migration-related-costs-at-over-86-billion-over-next-four-years-1467392402
REVEALED: Calais Jungle has cost France nearly £200m - and is about to cost £100m moreSource: express.co.uk/news/world/724552/Calais-Jungle-migrant-refugee-crisis-cost-France
Refugees Will Cost Sweden $18.6 Billion This Year-9.3x Over-BudgetSource: nationaleconomicseditorial.com/2017/02/10/sweden-migrant-crime-cost
Now imagine using these BILLIONS towards not only pensions but job creation programs FOR THE NATIVE POPULATION!
Economics is about choice. I'm not surprised I have to explain this to you.
Thirdly, although companies are in a race to the bottom with wages (and moving to automation to eliminate wage costs completely) it is the banks that need migrants as well. Why? Because Western economies run on debt. Even though pensioners are living longer they don't spend money even if they have it. Look at what old people mostly spend their money on; they buy bread and get their hair cut. You can't run an economy on that.
It's younger people who will have a need to buy or rent properties, buy cars and keep fueling them, buy clothes and replace them, etc. It's not all cash based anymore either. The banks don't give a toss about someone's pension. They do however need revenue and that comes from issuing credit to debt slaves and they don't care who they are or where they come from. Not enough locals? Lobby the government to bring in migrants. That's how the system works boyo.
within a few years, we could have a Ukrainian minority of 20% in Poland, which would be fantastic for ensuring that right wing Polish politics stay forever in opposition.
You sound like Erdoğan's soulmate when it comes to migrant influence in a host country. So it's not surprising at all that you admit you believe immigrants in Poland should be given rights like voting but should never truly integrate so as to ensure a left wing voting block that will effectively result in a leftist one party system that rules forever. Dream on! You conveniently forget that Polish dissidents came about during the communist era and they rose above their oppressors. Today they are regarded as the heroes and your ideology is held in contempt.