Appears to be C++11, which is contained twice in your list. C++20 doesn't exist yet. C++17 isn't finished either.

It doesn't appear to use new language features, only some library things like std::unordered_map, from what I gathered in a quick look. Most things will probably work just fine with C++03.

If this would be in Python, for example, for starters we would need to know if it is 2 or 3 variant.

Then we would need to know which of the following versions is being used:

    Python 1.0 - January 1994
        Python 1.5 - December 31, 1997
        Python 1.6 - September 5, 2000
    Python 2.0 - October 16, 2000
        Python 2.1 - April 17, 2001
        Python 2.2 - December 21, 2001
        Python 2.3 - July 29, 2003
        Python 2.4 - November 30, 2004
        Python 2.5 - September 19, 2006
        Python 2.6 - October 1, 2008
        Python 2.7 - July 3, 2010
    Python 3.0 - December 3, 2008
        Python 3.1 - June 27, 2009
        Python 3.2 - February 20, 2011
        Python 3.3 - September 29, 2012
        Python 3.4 - March 16, 2014
        Python 3.5 - September 13, 2015
        Python 3.6 - December 23, 2016

And for extra fun we can also add PyPy, CPython, IronPython, MicroPython, .... into the mix.

I can gladly play this game with any other programming language.

Languages that people care about, get new versions all the time, and not all tooling implementations or developers catch up at the same time.

It is part of our job to deal with it.

Email the author and ask? After he tells you, then use -std=c++XX (or similar) on your favorite compiler and you'll be fine.