I have heard that there might be a Buffy the Vampire Slayer season 8 on DVD, but not directed by Joss Whedon.
Is there any news about if it´s gonna happen or not?
I also heard something that suggests the first writer (not Joss!) didn't do a good enough job and therefore it was put on hold until they could find a new writer.
Why isn't Joss Whedon writing it himself? I mean, he is the writer of all the other Buffy episodes!
Buffy Season 8 was written by Joss Whedon (along with several of the other writers, like Jane Espenson). However, it was a comic series, not a TV series. There was a motion comic series made of it, which according to Wikipedia you can get on Amazon or iTunes, or on Blu-ray or DVD.
It sounds to me like you are confusing a Buffy Season 8 DVD release with the planned re-make of Buffy The Vampire Slayer, the movie. The history of the movie seems to fit all of the criteria you listed in your question.
The original movie was written by Joss Whedon but he has very little involvement in it otherwise, and the director of that film made quite dramatic changes to it. (If you are a Buffy fan, that last part should read "absolutely butchered and destroyed it" though I don't actually know what the original script looked like).
Thankfully, Whedon was able to re-boot the idea as a TV series, under his own direction, and presumably take the concept more in the direction he intended.
In order to get the original movie made, Whedon gave Mr. and Mrs. Kuzui (the original director and producer) a portion of the rights to the name. This includes the rights to the movie version of the character, rights to use the name, and executive producer credits on both Buffy and Angel (despite, AFAIK, neither having the slightest involvement in either series.)
In the past few years, the Kuzuis have announced plans to re-make the movie, not as a sequel but a full reboot. The plan is to do so without any participation from anyone involved in the TV series, including Whedon or Sarah Michelle Gellar. They have also stated that they have no intention of holding to any of the continuity developed in the TV series nor the Season 8 and 9 comics; this would essentially be a new, completely separate Buffy universe. Since they own the movie rights to the character and story, there's nothing Joss can legally do to stop them.
The last I heard, the original script submitted to the Kuzuis was rejected and they were looking for a replacement writer, but that was at least a year ago. Given that the presumable target audience for such a movie have almost universally pledged never to go see it, its possible that the film has been silently dropped, but officially it's still "in the works".
