Hi Youri!
So far as I know we’re still waiting on some additional files as requested by Leah in that other topic. Once we get those we’ll test them and – if all goes well – we’ll roll them into the next suitable release.
If you’re really keen to use them before that point, you can – it looks like Mario posted a publicly accessible .zip of his translated files and I’m sure you’re welcome to use them – however putting them in place on top of the existing release is not something we can help you with here.
The following URL links to lots of useful resources about translations in WordPress and much is applicable to our own plugins – so it could be worth checking it out if you want to give it a try anyway:
make.wordpress.org/polyglots/handbook
However, if you are at all unsure I’d recommend waiting until the next official update.
Thanks!