Scala code can be used in Java projects and vice versa, so this issue might instead be labeled "Java Admin SDK".
But, I'd argue to code it in Scala, because Scala deploys everywhere Java does, but the stronger type system is great for safety in financial/blockchain applications, and Scala can additionally compile to JavaScript via the excellent Scala.js compiler.
I'd be happy to contribute to a Scala SDK. I write Scala every day.