I’ll give it to Tog, the UI is creative, and it communicates its intention without words, but it’s awful to use. It feels like fighting the computer to choose a selection even after you learn the trick.
I tend to agree with other commenters here that it's better to just make a checkbox list and require one to be selected. Or in cases like language, maybe have a primary radio (mandatory) and a secondary checkbox (optional) section, where you need to select a language for the app to show you thinks in but can indicate interest in other languages' content.