If you have a good product new engineers will learn whatever language it is in. This very article is a perfect example. I'm sure Slack isn't hiring kids out of college with extensive PHP experience.
Php is pretty easy to pick up. We have way to many languages (Java ,Perl, php and python)
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.
