I looked from the source code where it printed error message like that and debugged error to missing ogre_plugins.cfg file. This problem was solved when I copied ogre_plugins.cfg from source tree to my datadir (default would be /usr/local/share/freeorion)
At the same time I wonder why bindir and datadir defaults are not relative to prefix (according to "scons -h")? Now I have to set all three separately to install freeorion to separate directory hierarchy.
The datadir and bindir *defaults* are necessarily determined in C++ code, and have to function even if there are no files available to provide them. The only way (I think?) to have these defaults change depending on the scons parameters would be to have the scons script modify the source code before compiling. This isn't very portable to other build systems.
There should be a way to get the actual binary directory, though, rather than using the current scheme of 1) trying the hard coded location and if that fails 2) hope it's the same as the working directory. Having this, all the ogre cfg files can be put there and should be reliably gettable.
Edit: There probably is, if my attached patch from a few years ago works as it's supposed to... /Edit
I don't think there's any sensible way to get the data dir, if it's not in the default location, though. We should probably add a command-line switch to specify this directory. Currently the workaround is, I think, to generate config.xml with "freeorion -g" and then edit that file to specify the data directory.
(...but segfaulted when I tried to begin playing)
There are a vareity of possible causes of this. To start, as OndrejR noted, do you have an ATI graphics card and does your card support OpenGL 2.0? If yes, once you get to the main menu and before starting the game, can you go into the options menu - from the main menu button - and go to the galaxy map tab, and disable galaxy gas rendering, starfields rendering, fog of war scanlines, and optimized system rendering, and then try starting a game? If this works, try enabling those options one at a time, to see if it will run with them enabled.
I'm slightly concerned that you'll have trouble launching the server or AIs, though given that their binaries will be in nonstandard locations that apparently the program has trouble dealing with...