I would suggest to raise this as feature request on Github: https://github.com/mendix/CKEditorForMendix
I would think you just need to do is change the config.font_names in the config file to point to a font family.
For example:
'MyWebFont'
And load the font as a CSS font family inside the widget css.
Or if you wish to use the font globally throughout your application inside the main app css or even a index.html stylesheet load.
@font - face { font - family: 'MyWebFont';
src: url('webfont.eot'); /* IE9 Compat Modes */
src: url('webfont.eot?#iefix') format('embedded-opentype'), /* IE6-IE8 */
url('webfont.woff2') format('woff2'), /* Super Modern Browsers */
url('webfont.woff') format('woff'), /* Pretty Modern Browsers */
url('webfont.ttf') format('truetype'), /* Safari, Android, iOS */
url('webfont.svg#svgFontName') format('svg'); /* Legacy iOS */ }