[nyh]

Some do, and some don't. OSv (https://github.com/cloudius-systems/osv), for example, is also a unikernel in the sense that it can only run a single application at a time (it has no kernel-user boundary, nor support for multiple isolated processes). But is designed to run any Linux executables (using a dynamic linker which is part of the kernel) so it is not limited to a particular programming language.