Comment 3 for bug 1613519

I would also go for the command line option. I've tried to look those packages in the Software Center and they don't appear. Synaptic package manager could be used instead (I found them there), but it is not explained in the manual, though it is mentioned at #1317 and appears in the glossary.
Anyway we could also go for the third option with just some rewording:

"To install these additional codecs, open the \application{Terminal} either through the \application{Dash} or the \application{Launcher}. When the \window{Terminal} window opens, use apt to install the following packages via \userinput{sudo apt install} (sudo apt install ubuntu-restricted-extras libdvdread4 libdvdnav4) or using the Synaptic package manager and looking for:"

I will watch this bug to follow the final decision in the Spanish translation.