Reading package lists... Done
Building dependency tree
Reading state information... Done
Package skype 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
All existing answers I found are for the pre-multiarch era (chroot)
https://help.ubuntu.com/community/MultiArch says it is OK to install i386 package on amd64 under the multiarch environment, but doesn't say how.