I'm unable to use terminal emulators (using i3 window manager), the only way I can use one is the Emacs shell mode.
When I try to open a terminal emulator from the Emacs shell, it gives some of the following messages:

In case of sakura: sakura: error while loading shared libraries: libvte2_90.so.9: cannot open shared object file: No such file or directory
Terminator: You need to install the python bindings for gobject, gtk and pango to run Terminator.
Xterm: xterm: error while loading shared libraries: libutempter.so.0: cannot open shared object file: No such file or directory

I tried installing libvte (http://www.linuxfromscratch.org/blfs...xfce/vte2.html), I downloaded the archive, untarred it, did ./configure in the folder, everything seemed normal at first, but then...

checking for gcc... gcc
checking whether the C compiler works... no
configure: error: in `/home/magnus/Downloads/vte-0.28.2':
configure: error: C compiler cannot create executables
See `config.log' for more details.

What does this mean?

The most fascinating thing about this is that yesterday, everything almost worked (opening terminal emulators did, configure scripts did not), and today, everything went horribly wrong for some reason.

The question is what did you change or what updated? Peppermint is a Buntu spin focused on the "cloud" so some development stuff may not be natively installed.

I didn't chaneg pretty much anything, but I tried to install Ruby on Rails the other day, and that's where the GCC problem began showing. The next day, starting a terminal emulator reported that "{library}.so does not exist". This happened to all libraries, apparently, including libperl and some others.

There's your answer. I assume it was an aborted install as you said "tried". who knows what was affected. I'm not a developer myself so I have no idea what damage could have been done. You can always reinstall a clean system and begin again. As I said before, Peppermint is kind of an odd duck and may not be the greatest system as a developer base with it's cloud focus and blend of DEs (XCFE window manager and LXDE environment)...