Answer: What’s the best language to learn for graphic design, aside from HTML?

I would first suggest CSS, so you can style any of the HTML you produce. With HTML and CSS, you can build almost any design you come up with.

After that, I would look into JavaScript, as it will allow you to begin adding interactive elements and nice animations.

For an example of these, check out a great list of frameworks (some JS, some CSS):

9 of the Best Animation Libraries for UI Designers — SitePoint

Happy designing!