Though a relatively new language, Flutter is a good choice of frontend widgeting.Coupled with dart backend, it is a thriving community that sees daily newcomers to learn the language.
Is it possible to get triple backward tick support for dart (flutter will be an assumed?)
Discourse does not manage code highlighting instead they use highlight.js. They already have dart and an admin needs to enable that language. And Flutter is not in the liberty and has not been requested it seems like.