@booze: Well you know the salary before you apply also you know the fleet and the bases available. The model is created with Polish cost of living and Polish taxes in mind and not for example Norwegian cost of living and Norwegian taxes. With a base in Poland you can get a better salary only in Ryan Air Sun / Buzz (they do actually pay extremely well (having Poland in mind) for captains at least) and also maybe in Wizz Air (sector pay is some strange way of calculating salary) too but you will not have the same opportunities to fly different aircraft plus possibility to get to long haul with 787. So its up to each person what they think is most important for them. Additionally I find it incorrect to compare salaries with bases in Poland with salaries in bases in some high cost nations, especially if someone desire to live in Poland then how does it help him that in UK he could be paid more if he do not desire to live there?
As for information about employees "discriminating" well I know pilots who just got a job there and instructors who are both FOs and Captains at LOT. No one have heard about things like this happening plus there is from what I heard so to say always a Polish Captain/FO flying from bases in Poland.
Regarding other airlines requiring their relevant language I have seen in discussions people write that they do not require native speakers but still prefer them than proficient speakers of the language who are not native. No one claimed it to be discrimination, but some people instead claimed things like for example British Airways should make some special hard English tests because its "unfair" that all pilots speak English and can apply to "their airline" instead of natives only.