Registered – sub group by language

Site runs in a number of languages & have set up various premium groups, defined by LANGUAGE + PRODUCT BOUGHT.

Model is a Freemium one, so we are also offering some free content to visitors if they just register. We will then capture email and hopefully upgrade them to premium later.

Understand that basic registrations are captured in the “Registered” group and have 2 questions related to how we can construct our email campaigns;

1. Is the Registered group this ALL members – ie does it include premium members who have since bought product too?
2. Can we automatically place new registrations into sub-groups of the “Registered” group – defined by language?
3. If not, how can we filter it, as we need to email the non-premium registrations with different language content / offers etc.

Interested to hear any comments.