I can code in Julia, Python, R and Matlab. It's just the ignorance of some from the AI field. R and Matlab might be good for prototyping but not for long running stable web server applications. Julia is still too new. Python syntax has spaces part of the syntax. And Python destroyed the community by splitting it in half - 2 and 3 are still around more than a decade later and many projects will never upgrade to 3, but moved on to Go.

Lua is used in Torch. Some are in C++. Unfortunately too many entry level samples are in Python. It's like the JQuery plague was to JavaScript not too long ago, when every other question on StackOverflow was answered with a slow as hell JQuery snip instead of vanilla JavaScript. Good that people moved on. I welcome the same for Deep Learning.