Close I think - the best language to use is the one you will have the easiest time hiring good talent for. If you found a startup and all really love and are fluent in COBOL that's great but... good luck when it comes time to hire another employee.
A lot of interns end up using php(symfony). If they know Perl or Java they can pretty much jump right in. Python they take a little bit though not much more.
I have yet to work a day job in Rust, but I've worked in Java, C++ and Go so I'd be quite confident applying to a Rust position as long as it wasn't specifically security focused... I would be less confident in how quickly I could pickup Prolog - I think my brain works well for the nuances of the language but I'm less certain.