This is a very annoying warning message when you run some old X applications, such as xterm, xfig, xdvi, etc. The short explanation is that you set your locale to UTF-8. It requires fonts to display various languages. It is hard for you to install all required fonts from the beginning. A long explanation can be found here. The easiest solution is to install font-isas-misc, font-jis-misc, font-daewoo-misc and restart your X, as suggested here.
It is now possible to use a font from a web server instead from the user's local machine. For example, Google fonts provides a lot of free fonts, which can be used in the css file. Once a web font is used to display a web page, the page will be shown with the same font in different browsers and OS.
Activities mentions in this site have been supported by the following grants: