The formatting specification language is already complicated enough without adding even more to it. As PEP 378 says "It is not the goal to replace the locale module, to perform internationalization tasks, or accommodate every possible convention."

Your best bet is to write your own formater and use that:

f'{formater(v)}'

You could also pass it whatever parameters you want, like specifying the number of digits or the separator or whether to use the locale to determine these things.

The PEP suggests Babel (http://babel.pocoo.org/en/latest/), which I don't have any experience with, but seems pretty complete.