I suspect that Oli’s original question was less about languages and more about the status of the SDK versus the more recent DevKit, both of which are primarily maintained on GitHub by Tim Place. For some reason the DevKit readme refers to the SDK as being ‘legacy’ despite there never having been, as far as I know, any official announcement of the DevKit’s existence (let alone any announcement that it was replacing the beloved SDK).
My own presumption at the moment is that DevKit is still a work in progress (e.g., few docs) and that the existing SDK remains the thing to use. Perhaps this will change with Max 8, perhaps not. For now I am happy using the good ol’ SDK.