The answer to the overall question "So tell me, what did they add?"
Through most of the riddle, the word "it" refers to:
Java (the programming language).
It may be too big to golf with
Not a particularly good code golfing language to use on Programming Puzzles & Code Golf Stack Exchange.
And that a shortest answer in it exists may be just a myth
Maybe refers to the general difficulty of Kolmogorov complexity? Or maybe, it could just mean that so far Java hasn't been the winner in any major code golf challenges?
But this week we've reached two
Java 10 was just released (and to computers, 10 means two... ?)
We've come a long way from
bar and ...
foo would fit here with the rhyming scheme, and from the general usage of
bar as meta variable names in computing. Not sure how it applies to Java in particular - but I agree Java has come a long way from its beginnings. I remember when it was largely used in small Java applets embedded into web pages, like the demo applet with the animation of the white triangular cartoon character (can't remember the name, might be misremembering details...).
And they've added some things new / Although only a few
Only a new features in Java 10.
One is pretty useful though / Similar to the sharp C we know
This would likely be "local variable type inference". Just like in C#, this is used by declaring
var as the type. That could certainly cut down on the length dedicated to explicit type declarations.
But although we will be shorter now / It doesn't matter much anyhow / We will never be able to compete with big short ones
Still doesn't really make Java 10 compete with the dedicated code golf languages.
So they will continue their memes and puns
Perhaps an oblique reference to the names of some of the dedicated code golf languages? Not sure here.
So tell me, what did they add?
Local variable type inference, in other words,
And how can this riddle be interpret?
As @Jordan.J.D pointed out in a comment, Java is largely an interpreted language (or at best JIT compiled) - especially now that GCJ has officially been dropped from the GNU Compiler Collection (and it was pretty much obsolete anyway for a long time before that).