And how well was Kotlin doing before it was backed by Google?

Very well. Google deciding to back it for Android wasn't some bold, out there decision. Android developers could already use kotlin, because of its Java interop. Google was just responding to pre-existing demand that the community was already generating.

That's why I don't think it makes much sense to treat kotlin in the same category as the other languages. Sure, it's a programming language, but the way JetBrains executed on it with its easy upgrade path from java and really excellent design, not to mention the toolchain, mean that it's success and trajectory cannot easily be generalized to other "weird languages".