Go inside "Edit -> Preferences" or press "F11" to access the preferences menu.
Go inside Application (1) => Skin (2)
Change the skin to a custom one by changing it's name (3) and then save this skin (4)
Now you can have access to the font choices (arrows)
Font Choice : Choose the font for the user interface
Fixed Font Choice : Choose the font for the texts editors inside of Smode (such as the text layer or the shader editor)
Do not forget to restart Smode for theses changes to be taken into account.
Recommended Fonts :
Chinese : Microsoft YaHei
Here is some websites to help you find your font :