Any reason why everything (algo, API, website) cannot all be done in the same language? If you that, it will keep your solution stack simple, which over the long term will reduce TCO. Lastly, I would also suggest using a Linux friendly language (Python, Ruby, Node, etc). These languages will reduce your hosting complexity and costs. They will also allow you to scale faster (when needed). If speed is needed, then consider using something like C++ for the algo and API. The web app can still be in the Linux friendly language.