The backend was in Go, a language that I have no idea about. Also this was in Japan and backend discussions and 3rd party vendors all happened in Japanese, which I also didn't speak. I suggested learning Go myself and try to help, but my manager was also against it.

I was dubious I'd be of much help when I suggested but at least I'd learn the language we were using and might be able to help long-term. But as things kept getting delayed I'm sure I'd have been able to learn enough to be of help even within that project. But again, had a hard ban to either join a different project or learn/help with Go, "just keep improving the front-end and integrate it with the backend and don't do anything else until that's done".