You can choose to program functionally in Java or Python! I do this enough that seeing object oriented Python irritates me. I see this as more of a stylistic choice than forcing new languages.
Spending time in Haskell really improved my programming in other languages. I now use a functional style by default. I program imperatively when I have to, as a conscious choice, like a code smell.
It's nearly always better for the project to choose a widely known and supported language, which will be Java or Python or some such. But learning how much can be done functionally when the language compels you to changes the way you look at it even when the language has imperative features.
I'm talking about features that FP languages have (like do-notation) and imperative languages do not, rather than the other way around (like enforced pure functions).
you cannot write Python like Haskell (for example) because Python lacks the necessary features.
