westfw:
First, "Arduino" is not a programming language. It's more of a "framework" based on standard C/C++
I'm very interested in this topic. When I first started with Arduino I though .ino files were written in Arduino language. As I realized how awesome microcontrollers are and made the decision to dive deeper into this world, I started looking at alternatives to Arduino. I felt that learning a proprietary "toy" language would be a waste of my time in the long run, as I reached the limits of what I could do with the language and decided to move on. Then I read that the Arduino language was C++. That was a big "aha!" moment for me, which made me confident that sticking with Arduino was the right decision.
When I've seen people talk about the Arduino language, it's usually done by beginners or people denigrating the Arduino project. I was aware that somewhere on the Arduino site they talk about the Arduino language, but I thought of that as perhaps just an attempt to make things seem less intimidating to a beginner who might just shut down at mention of C++. My belief was further reinforced by a Hackaday article from Elliot Williams, who always writes excellent articles:
Over the years, I've corrected people talking about the Arduino language here several times. I've thought that the impression that there is an Arduino language and an "Arduino compiler" was harmful to the learning process and led to misconceptions (perhaps like this discussion).
Recently, I submitted a proposal to Arduino about adding some text about C++ to the Arduino Language Reference pages. I was informed by a couple of very knowledgeable Arduino employees, whose opinions I respect, that .ino files are written in Arduino language, not C++:
I understand the sketch preprocessing process, but I never thought that it made enough of a difference to qualify the code written in .ino files as a new programming language. This made me realize that I have no clue where the line is on what becomes a new programming language. Although I've seen well thought out arguments about why there is no Arduino language, I've never seen one arguing the contrary. It would be interesting to see something like that written by someone knowledgeable on the subject of programming languages.