Well, around the internet, they float around some NOT PROFESSIONAL, translated in ENGLISH, versions of the Witcher books, that still have not been translated and available for sale in English language. And people posted links in forums for downloading them. Also, the Kat (meow) has them hoarded away.

Well, is it considered piracy and theft to download those books? It seems the amateur free sharers have already translated ALL books/stories in existence, with the sole exception of "Something Ends, Something Begins", and the latter is neither in the witcher world, nor cannon, in its entirety.

Should we grab those books? Or not? How, and why?

I know that there are published versions of some of the books:

The Last Wish
Blood of Elves
Time of Contempt
Baptism of Fire

with the next one that I'm aware of being due in mid 2016

Sword of Destiny (lies between The Last Wish and Blood of Elves).

There is no reported publication date for the remaining 2 books of the saga, nor the final volume of short stories.

The Tower of the Swallow
The Lady of the Lake

Storm Season.

I would consider it incorrect to use a "fan translation" of the four published volumes, or to continue using Sword of Destiny after it is published in 2016... but have been very happy to have been able to read these in English in the absence of adequate interest from English Language publishers... (not tried Storm Season yet, but I'll probably wait till it is available in full).

In any case, the entire bibliography of the witcher, fan-translated to english, is in Kat (meowow). Anyone who writes "Witcher books" cannot help but stumble upon them. Even the Tower of the Swallows and the Lady of the Lake are English-fan-translated.

If you're asking about the morality of the situation, I can't help you there. If you're asking about illegality, then I think that the argument that the copyright holder would make is that the fan translation is a derivative work, which is encompassed by their copyright, so downloading the fan translation would constitute infringement.