When editing user lessons or lesson courses in the editor the font size is much to small when haven a thai lesson (and presumably other lessons with similar fonts. There seems to be no way to change the font size. Being rendered with the font highlighted makes it even harder to read it, though this can be changed by changing the keyboard layout to the one belonging to the lesson. I just filed another bug, where I described this problem: The Popup-window do not adopt the keyboard-layout of the parent window. You can easily test it, if you change kde keyboard layout setting as per window. Reproducible: Always Steps to Reproduce: 1. Open a lesson in thai Expected Results: Maybe a button to change font size?
KTouch uses for its editors the system's default monospace font. On KDE Plasma Desktop it can be set through System Settings. To temporally increase the font size, zoom with Ctrl + Mouse wheel.