Why make new #fonts

I subscribed to the blog of UnderstandingFonts. An organisation that is in the type design training business. One of the questions they obviously ask is "Why make new fonts ?". Obvious because when there is no reason for more fonts, there is no reason for their business.

The arguments they provide are good. They are applicable to Wikimedia projects as well. It does make sense for Wikisource or Wikibooks projects featuring historic content to have a font that reflects the historic character.

The problem with fonts is that they are often incomplete. Typically a subset of the characters of a script are selected. When a font is freely licensed, it is possible to add to the existing work and add those characters that make a font usable for another language.

This is of particular relevance for the fonts that will be used as web fonts by the Wikimedia Foundation. At that, it would be good to have a tool that checks for what languages a particular font is usable.
Thanks,
       GerardM