I did a fairly lengthy explanation of what the IDE does to your sketch here.
The fact is, the .ino file is treated as C++, and is modified by the IDE pre-processor slightly to automatically generate function prototypes.
So, Arduino is not a language. You may as well argue that the output from the Visual C++ "wizards" are a new language. But they are not. The wizards just generate C++ for you.
@curious48 - you mention std::vector. That is a library (the Standard Template Library) which is written in C++. It is not, itself, part of C++. It is a library written in C++. Just like the works of Shakespeare are not a new language. They are written in English.
You can install implementations of the STL on the Arduino, and then you have std::vector (and std::map etc.). The same thing applies on "normal" C++ installations, except that they may have installed the STL for you, so you confuse the library with the language.