the reason these companies hire people from third world countries (if you consider france spain germany netherland canada .....) is the languages capabilities
Exceeding unlikely if you mean third world country such as Nigeria or India. By far the highest criterion is that they can pay very low wages, so low that the employees are "trapped", which reduces turn-over. As a matter of fact, anyone considering working for a BPO should always bear in mind that BPO is exclusively about reducing labor costs, and that that will always be the number one criterion in ANY interaction you will have with the company.
You can get up to 5000 PLN gross salary
Very, very poor wages. That's a measly $12,000 US net, or about minimum wage for burger flippers in the US. Not worth relocating to Poland for, certainly not for anyone from a first-world country, and not even for a recent grad from a third-world country. There are plenty of better opportunities elsewhere. Getting paid that low means that you are trapped: unable to save up enough to relocate to a better job elsewhere. I made more than that as a teaching assistant in graduate school in the States twenty-five years ago, teaching only two courses.
But why all these third-world workers claim (and there is an avalanche of them on this forum) they get hired for salaries which are completely unreal?
Those "unreal" salaries are quite low and not at all attractive to non-Poles. For example, 10,000 PLN gross is the equivalent of $40,000 a year in the States. You're not going to find anyone at that level of qualifications and experience that will get even out of bed for less than $100,000 in the States. And even native Poles at that level are highly tempted to move west, and a good many do. Hence the high turnover and shortage of native Poles willing to take these jobs. For the time being, it seems to make economic sense to hire third world workers and bring them to already existing BPO centers in Poland than to build BPO centers in even poorer, but often highly unstable third-world countries with ghastly infrastructure. BPOs in Poland seem to be in sort of a sweet spot at the moment.
There are several other factors at work:
BPO workers form third world countries are often desperate to take any job, even one in Poland. Even with its low wages and poorer living conditions, Poland is heaven compared to, say, Uganda, Nigeria or Pakistan.
BPO workers from third world countries see any job in Poland, no matter how bad or poorly paid, as a back door to a better future elsewhere in the EU. A lot of them seem unaware that Poland is quite poor compared to the Western European countries. Actually, a lot of posters on this board from Portugal, Spain and Malta seem to think that Poland is part of the "Rich North".
BPO workers are often not aware that there is little, if any, opportunity for advancement in these jobs, and they are cut off completely from the corporate ladder. And that there is very little opportunity to improve one's qualifications in Poland.
In short, Poland is a seemingly perfect short term "solution" for the desperate and hopelessly ignorant, and since there is not shortage of either of these on this planet, especially in third-world countries, BPOs are making hay while the sun shines.