For adult sites? As most others advised, learn PHP + Javascript (HTML5+js+PHP) and you'll be happy. Optimised traffic trading servers are written in C, quite confusing one
I can not understand the Ruby mania myself, perhaps I am too old.
Python is cool and I use it to write my evil small scripts, but despite since a few years I always try to have new projects to be started from scratch in Python, in reality my (adult) productions sites are all based on PHP (even if may include also node.js or wowza=java pieces), mostly because they evolve from legacy PHP code pieces (cam sites, tubes or whatever).
I have mainstream services (no adult) with Java server (j2ee subset jsp/servlet), these was setup in late 1990's and early 2000s, and still up, but I would not advise Java on server really now, unless you are a bank or telecom... Java it was not updated in last 10 years - people use JVM more with Scala or such. A former java developer is now into C# and microsoft stuff, guess what.
About the deprecated PHP things - yes had to replace a few things on updates, but Python made even bigger changes! I mean tell me what you can update without issues.