@mathjazz - It looks scary, but it's really not.  The default is to be very cautious on what gets served to users, if a font for a locale is not found or enabled, the full font set (what is currently served to all users) will be used.

@ozten - I see what you are saying about enabling/disabling locales in one place, but locales currently do not map 1:1 to directories. 2 locales could map to the same directory. For example, both hungarian and russian could use the cyrillic font set. We could force locales to be 1:1 with a directory and use symlinks from locale->font directory, but we have to worry about Windows developers. 

Additionally, there are no adverse effects if a font for a locale is enabled, but the locale itself is disabled for Persona. No extra bytes are served to any users. The locale mapping here is locale->directory.

There is the additional issue that it is fine for a locale's font to be enabled in the font server, but the locale itself be disabled in the Persona configuration. Additional configured font locales will have no adverse affect.

Maybe like you say, all this should be abstracted into a connect-fonts-opensans npm module and the configuration is not needed here. I am heavily leaning this way. Would you be willing to lend me an ear and some of your ideas to get that moving?