In theory, you can write another language frontend for the Dart VM, but it isn't being utilized a lot as I can tell.
Here's a year and a half old page describing the Dart VM's internals: https://mrale.ph/dartvm/
Also, here are two examples of different frontend add-ons for the Dart VM, although outdated: https://github.com/thosakwe/bullseye and https://github.com/jvasileff/ceylon-dart