The collection has been out in the USA and in Asia since October 2018 and was announced for those markets in Gamescom a few months earlier. Surprisingly, Bandai Namco declared that the collection wasn’t for the European market — at the time. Since then, both Amazon Italy and Amazon Germany have put up listings for the Dark Souls Trilogy collection for both PS4 and XB1, priced at EUR 69.99 in Germany and EUR 71.99 in Italy. Both sites say that the release date is March 1st 2019.
On Amazon UK, you won’t be able to find the European version yet; you will find an imported US version sold by Amazon US through Amazon UK. Undoubtedly, it’ll be replaced by the new version either when it’s officially announced or a few days earlier, even.
The Dark Souls Trilogy collection — according to Amazon DE — includes Dark Souls: Remastered, Dark Souls II (and all of its DLCs), and Dark Souls III: The Fire Fades Edition, as well as all of the corresponding soundtracks. This means that buying the collection is quite a bit cheaper than buying all the games separately.
Bandai Namco hasn’t officially announced the collection for the European market yet, but we’ll most likely hear something from them in the next few weeks.