If you set language to something that Windows build does not support, the build appears to be stuck in “booting” status, and never starts. Example: https://travis-ci.org/mmozeiko/meow_hash/jobs/450156538
It would be nice to get error message, and fail the build if “language” is not supported.
I had it set to “minimal”, because that’s what I use in other matrix entries for linux/macOS. It took me a while to figure out that only shell/sh is supported (as described in docs). Example of successful build: https://travis-ci.org/mmozeiko/meow_hash/jobs/450166406