I am completely stuck in how to start parsing these kind of files in PHP. These are some sort of arrays with variable amount of sub-arrays. https://developer.valvesoftware.com/w
Late answer, but just saw this. The data on question is in (Valve Data Format)[https://developer.valvesoftware.com/wiki/KeyValues], also called KeyValues format, and is very reminiscence of JSON.
About a year ago I wrote this script which can convert VDF data to valid JSON. You can use it once and store the generated JSON or call it anytime you need JSON from VDF.
https://gist.github.com/AlienHoboken/5571903
There an online one I found. http://rossengeorgiev.github.io/vdf-parser/
The repo has a js and python implementations, it shouldn't be too hard to port them to PHP.