@lleo hey. Ubuntu 12.04 is 4 years old, so you won’t be able to run the latest versions of specialized software on it, at least not without some greasy work under the hood. The instructions I linked you to are simple to follow and worked well when I wrote them, but by now I doubt they will work in Ubuntu 12.04, for example because Ubuntu 12.04 only ships GCC-4.6.3 while RawTherapee now requires minimum GCC-4.9.
http://packages.ubuntu.com/precise/allpackages
While it is possible to upgrade the version of GCC in 12.04, I won’t link you to the easily googlable instructions because you can break your system.
As I replied to that person, the correct thing for you, a user, to do is to ask the people who run the distribution you chose to use to add the latest version of RawTherapee to it, if possible. Have you done that? And have you checked RawTherapee - Downloads and contacted the person who runs the repository?