Using SuperLab 4.5.4 on Yosemite or higher, you cannot edit fonts. This is a known incompatibility between 4.5.4 and newer Mac systems. Our development efforts have moved to SuperLab 5 nearly three years ago and we can longer fix this in SuperLab 4.5.
Whenever an issue with Japanese or Chinese or Korean has been reported, it has always eventually been solved by choosing a different font face. However, because you cannot change the font on Yosemite or higher, try changing the font on another Mac that is running an earlier version of the OS and then move the experiment back to your MacBook Air.
Have you considered upgrading to SuperLab 5? It is really a worthwhile upgrade, and for now, the price is only 50% of what a regular license costs. Plus, you will get a free upgrade to SuperLab 6 as well. The chance to upgrade at 50% off will end this September 30, 2016.