Looks like you get a runtime explosion mad then some. Your CI will need all of the runtimes used plus the extra code to handle multiple language runtimes in Pulumi via the automation api.
Anyhow, thanks for the link.
I guess typically you would pick one language and use that throughout the Pulumi project.
As would I. I see this becoming a pain for the operator of the build systems in a mutli-team environment.