[Sean1708]

  > Currently, yeah, just JS.

How do they plan to make it support multiple languages without having a backend service?

[jsjohnst]

There are a number of projects for transpiling X language into JavaScript. Most aren't super robust, but generally good enough for basic purposes. I feel once WebAssembly gets more steam, this will get even more robust.

Not claiming this is a good solution, but definitely would be one possible route.