Disclaimer: I have no idea if the title is true or not. There are no world cups for languages competing against each other for the trophy. What I do know is that X++ has taken some gigantic leaps forward lately in terms of extensibility – if someone decides to host a world cup; I'd be happy to sign up X++ for the contest! And by the way: Isn't X++ the perfect name for the most eXtensible language?
"Extensibility" is an overloaded term. In this context it means the ability to extend code from another library without editing their source code – in a manner that allows multiple extenders to live side-by-side without risk of collision.
Here is a top-ten list of the extensibility features in X++:
The innovation outlined above is driven by the need to deprecate source code editing of other's libraries (overlayering is just glorified source code editing). This has only been possible as we are in full control of the language and compiler. A strong justification for keeping a proprietary language alive and kicking.
For visitors not familiar with X++, let me mention that X++ is a .NET language; the compiler emits IL code; the CLR is the runtime. The language is used to write business applications in Dynamics 365 for Finance and Operations.