That's nice somebody enjoy polish language too
Than I think I can recommend polish female siger
Gaba Kulka. She is little bit inspired by Tori Amos and Kate Bush, sings in english and polish.
Now something from another genre and from my country
Here is one czech (moravian) folklore band that I enjoy - Tomáš Kočko & orchestr.
And also one metal band -
Silent Stream Of Godless Elegy
They were doom metal but now it's inspired by pagan folk music. So it's mixture of doom metal and folklore. But still not "typical" folk metal.
They sang in english but now their last album is in czech language.