Mod misses a clearly defined user-level locale

[marchant]

UserIdentity has a locale property.
But Mod's missing a clear entry point where to get it, even an anonymous one which should be created by default.
Application's object should be de-emphasized as we have better defined objects around, like environment, which apply equally well to a worker or a client-side / user mod.

But environment lacks both a locale and an identity property. A worker's identity should be the one of the service account running it for example.