Not sure about Ruby, but Python is a pretty popular choice. There are tons of open source projects that are used by big players for data processing and complex backends.
Might be used for that, but Python certainly wasn't "designed for long-running processes or data processing at first" which was your original argument.
These 3 languages are pretty comparable in many ways.
Unless you're doing matrix multiplications, PHP will work reasonably well. It's probably not the right tool for the job (because python's data ecosystem is too deeply entrenched in the ecosystem), but if your codebase is already in PHP, you can easily do long running processes in PHP (similar to how you'd write Rails jobs with ActiveRecord queries in Ruby).
