I'm trying to install Solarus DX on Ubuntu 14.04 Trusty 32-bit

the Solarus debian package depends on
libstdc++6 4.9
As far as I can tell, this is not released as a 32-bit debian package yet, not even for testing. Only 4.8 is available.

[Christopho]

Hi,
Solarus is supposed to compile with 4.8 indeed, so I think we should fix the debian package. I have just reported the problem to Nate-Devv, the packager.
In the meantime you will have to compile it yourself

[Nate-Devv]

Sorry I've taken a long time to reply.  There is actually a libstdc++ version 4.9 package in Debian Jessie (Testing) here. This is the reason why the package got compiled using libstdc++ version 4.9, as I run an up-to-date version of Debian Jessie 64-bit on my machine.

The packages are also hosted here, where there are also source packages if you would like to put libstdc++ 4.8 on your package.  The package will tell you what you need to compile it, and the compilation directions are in the repo.  I cannot myself compile it with libstdc++ 4.8 because of technical reasons I will not get into here.