Here’s a great
defaults write option for setting Markdown as the default language for any newly created BBEdit documents.
defaults write com.barebones.bbedit DefaultLanguageNameForNewDocuments -string "Markdown"
Whether you go File > New > Text Document, or have a scripted hotkey, by setting this you won’t have to change the language manually to get pretty syntax highlighting for you Markdown files.
You can find more of these options in BBEdit by going to Help > BBEdit Help > Expert Preferences.