How can I read every DVD, even if encrypted by CSS or other?

You can't be sure that you will be able to read every DVD.

libdvdcss2 will allow you to play, copy and rip DVDs encrypted with CSS (Content Scramble System). This is by far the most commonly used DRM on DVDs.

However there are other methods which are much more nasty. The ones I have come across were where some sectors of the DVD were deliberately corrupted so that they couldn't be copied. For these I used ddrescue which is a command line app similar to dd.

This program was designed for rescuing data from failing drives where there are accidental bad sectors. They can also be applied to get rid or the DVD DRM. If I remember rightly, this is the command:

ddrescue -d /dev/dvd ~/dvd_backup.iso ~/dvd_backup.log

You can then mount or burn the ISO file.

For legal reasons, DVD decryption is not provided by a standard Ubuntu installation

However, you can install libdvdread4 which has a script that allows to install DVD decryption

sudo apt-get install libdvdread4
sudo /usr/share/doc/libdvdread4/install-css.sh

OR

Add the medibuntu apt repository

sudo wget --output-document=/etc/apt/sources.list.d/medibuntu.list http://www.medibuntu.org/sources.list.d/$(lsb_release -cs).list && sudo apt-get --quiet update && sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring && sudo apt-get --quiet update

And directly install libdvdcss

sudo apt-get install libdvdcss2

Both methods may not be legal in every country (as far as I know, it's not legal in USA, but it's legal in Germany)

For a completely legal way buy the Fluendo DVD Player as posted in fluteflutes answer

One way to do this is using the Fluendo DVD Player available (for $24.95) in the Ubuntu Software Centre. This would ensure you can always play all DVDs as it is software supported by a company.

NB: Purchasing this also has the side effect of protecting you from any legal issues.

NB2: I'm sure someone else with more knowledge than me will be able to give you a 'free' solution.