sudo apt-get install libgtkmm-3.0-1:i386
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package libgtkmm-3.0-1:i386 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  libgtkmm-3.0-1v5:i386 libgtkmm-3.0-1v5

E: Package 'libgtkmm-3.0-1:i386' has no installation candidate