In real world practice, I can't imagine anybody ever saying "Different politics are possible." anyway. "A different political solution/result/conclusion is possible" is somewhat more likely. "Different politics is possible." is even less likely even if syntactically more correct :-) .
A different politics is possible. was mine and it was rejected with - Different politics are possible., A different policy is possible. - being the two alternative answers given. But treating politics as a singular is very common in English. For example, this article from the British Academy, "Building a new politics?" In the same way as a new politics, a different politics would be used. If the Polish is meant to be only that a different policy is possible then that would be the different, but it doesn't seem to be from the translation here.