I haven't created a programming language per se, but I created https://mypost.io/ which is a bit more advanced than most single webpage creation platforms, as it allows HTML, CSS, and JavaScript. With that--I basically added hundreds of lines of code to accept BBCode. From random strings and names to advanced mathematical equations and formulas. I mean, I didn't write the scripts per se, as I'm using javascript code, available on the Internet, but I did write the BBCode that makes them all easier to write out and publish on the website. For the math, however, I'm still writing up the documentation.