Restore Polish translation
@piotrdrag I noticed that the Polish translation got removed in commit 7fde2cd5 in 2015.
I do not really see the reason for the removal. Sure, it was incomplete, but so are a lot of the other languages.
On our testing website we have added the percentage completed for all languages. With that, it should be clear for users whether it is usable for them. Seeing an incomplete translation may even give some of them an incentive to help out on improving that. (We can always hope can't we.
My suggestion is to restore the Polish translation (I can take care of that), but I wanted to hear your opinion, since you were the one to remove it.