I am not aware of any way to customize Illustrator's built-in font grouping (and I would be surprised to learn there is a way), but it sounds like you could use a font manager application.
A font manager enables you to build your own "sets" of fonts, using any criteria you choose. Those sets can then be activated as needed rather keeping all fonts active all the time.
This is particularly advantageous if you have a lot of fonts. Since fonts that are not in active sets are essentially not installed as far as the OS is concerned, you reduce some system overhead and might benefit from a bit of performance increase. (At the very least, programs, like Illustrator, that enumerate all installed fonts at startup will load more quickly.)
A Google search with keyphrase 'font manager' will turn up a number of choices. I cannot make any specific recommendations because my font manager is the now-defunct Adobe Type Manager Deluxe -- a program I will miss if and when I upgrade from XP.
You cannot change specific Unicode/ OpenType features (including font family and region), as it would require to modify the font itself, nor can you influence how most programs present their font lists (since they are populated dynamically and don't work on static font groups). Using a font manager should help you in organizing your fonts, though. Sophisticated ones like Extensis Suitcase can easily manage a bazillion of them and enable/ disable sets on the fly. Suitcase will even go so far as to allow you to have most non-system fonts disabled and then auto-enable it when you drag its preview into an application program...